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1: Tube DIY Asylum, Direct-cupled DHSET can be tricky (0.00)
Posted by Paul Joppa on 2024-04-13, 08:53:32 (98.59.249.131)
The only thing I've run across that needs some thought is directly heated tubes with indirectly heated drivers that are directly coupled. Some tubes are more sensitive than others, and some circuits a .......
2: SET Asylum, RE: On keeping Bottlehead Paramounts alive! (0.00)
Posted by Paul Joppa on 2024-03-27, 21:03:50 (73.42.214.122)
Cycling the power too quickly usually takes out the Zener string, and probably a transistor in one of the current source boards. I suggest posting on the Bottlehead Forum for more detailed diagnostic .......
3: High Efficiency Speaker Asylum, It's the 10dB shelf filter ... (0.00)
Posted by Paul Joppa on 2024-02-27, 20:41:19 (73.42.214.122)
... that cuts the screechy lower treble. Without the filter, you can have 103dB (above 2kHz). Many highly-regarded "efficient" fullranges have this issue. Few are much better than 92dB/W/m in the pist .......
4: Tube DIY Asylum, RE: data sheet says 400v (0.00)
Posted by Paul Joppa on 2024-02-13, 07:39:53 (73.42.214.122)
It is high; most tubes are rated for 300v maximum. But a few are higher - for example, a 6SN7GTA is rated at 450v. .......
5: Tube DIY Asylum, data sheet says 400v (0.00)
Posted by Paul Joppa on 2024-02-12, 16:51:28 (73.42.214.122)
The maximum plate-to-cathode voltage in the JJ data sheet is 400v; the maximum heater-to-cathode voltage is 200v. .......
6: SET Asylum, RE: Ongaku and Output transformer (0.00)
Posted by Paul Joppa on 2024-01-13, 21:24:01 (73.42.214.122)
You have accurately guessed what I'm listening to, in spite of my garbled post :^) It's a custom Paramour-like amp with 6C5/6J5 driver and Stereomour/S.E.X. plate chokes and outputs. The iron, includi .......
7: SET Asylum, RE: Load Z (0.00)
Posted by Paul Joppa on 2024-01-13, 16:38:01 (73.42.214.122)
My measurements are very simple-minded, not a "full measurement" by any means. Just an oscillator driving a resistor in series with the primary, with all secondaries and magnetic core shorted together .......
8: SET Asylum, RE: Load Z (0.00)
Posted by Paul Joppa on 2024-01-12, 22:39:28 (73.42.214.122)
Only if you use the same operating point. That would cut the available power nearly in half; I don't think there's a big market for 4-watt 300B amps ... I have used 4K impedances with 2A3s, but I adju .......
9: SET Asylum, RE: Nice OPT (0.00)
Posted by Paul Joppa on 2024-01-12, 22:12:25 (73.42.214.122)
These measurements illustrate what I said below about excessive interleaving increasing and complicating the transformer parasitic capacitance(s). For what it's worth, I recently designed an experimen .......
10: SET Asylum, RE: Nice OPT (0.00)
Posted by Paul Joppa on 2024-01-05, 07:37:56 (73.42.214.122)
If you are going for the ultimate performance, I agree. The most appealing approaches to me are either bi-amping (i.e. a subwoofer with separate amp) or parafeed with a high-power current source to re .......
11: SET Asylum, RE: Nice OPT (0.00)
Posted by Paul Joppa on 2024-01-04, 22:47:51 (73.42.214.122)
In my experience, the reference for good bass with 300Bs is the Magnequest FS-030, which has about 40 henries inductance with generous flux headroom and small copper losses. That means it weighs about .......
12: Tube DIY Asylum, RE: Modification of a Heath W5-M - Help and advice (0.00)
Posted by Paul Joppa on 2024-01-01, 10:17:06 (73.42.214.122)
Another helpful resource: This covers many of the design issues uncovered since the introduction of the W5-M (in 1956?) .......
13: Tube DIY Asylum, RE: No can do? (0.00)
Posted by Paul Joppa on 2023-12-19, 07:42:55 (73.42.214.122)
20% over current is 44% over power, and the 2xx series is not exactly conservative in their ratings. I wouldn't do it. You might get away with it if the other windings are underused and the thermal co .......
14: SET Asylum, RE: Never got too excited about the sound of the Paramour... (0.00)
Posted by Paul Joppa on 2023-12-10, 22:24:32 (73.42.214.122)
Thanks for the kind words! Yeah, the early Paramours were severely constrained by cost (the output transformer was a $4 70-v line unit!) - cheap and cheerful. LF power band around 100Hz (3.5W). It was .......
15: SET Asylum, RE: Not necessarily (0.00)
Posted by Paul Joppa on 2023-12-09, 21:40:36 (73.42.214.122)
A dozen years ago or so, we (Bottlehead) changed from a 12AT7 driver to a 5670 driver in our 300B amp. We found virtually no difference in the distortion spectrum, though the data sheet plate curves f .......
16: Tube DIY Asylum, I should just mention ... (0.00)
Posted by Paul Joppa on 2023-12-04, 11:44:43 (73.42.214.122)
It depends a lot on the impedance level desired. In my (limited) experience, plain windings with no tricks are good enough for outputs below 3-4kOhms primary - usually less than 500pF. Capacitances ar .......
17: Tube DIY Asylum, RE: Divide it Axially (0.00)
Posted by Paul Joppa on 2023-12-03, 14:56:29 (73.42.214.122)
I never got the full story, but I think there were a couple tricks to reduce capacitance. One was to add some teflon between layers, and the other was to use bifilar windings. Many of Mike's chokes we .......
18: Tube DIY Asylum, RE: Divide it Axially (0.00)
Posted by Paul Joppa on 2023-12-03, 07:54:04 (73.42.214.122)
I remember those winding machines! A friend had one, some 50+ years ago... According to the Wikipedia article on inductors, that criss-cross winding is also called basket-weave, or honeycomb. It's ano .......
19: Tube DIY Asylum, RE: Divide it Axially (0.00)
Posted by Paul Joppa on 2023-12-03, 06:54:28 (73.42.214.122)
Yes, exactly. There are multi-chamber bobbins available for this purpose - I believe I've seen pictures of as many as eight sections. .......
20: Tube DIY Asylum, RE: Does the plate load choke need to be sectioned (like interstage)? (0.00)
Posted by Paul Joppa on 2023-12-02, 06:51:31 (73.42.214.122)
There is no way to use interleaving in a choke. There are however two main ways to reduce the capacitance in a choke: 1) divide it axially, in many sections in series 2) put a layer of insulating pape .......
21: Tube DIY Asylum, RE: Technical Question, How to calculate cathode bypass cap value if the cathode is elevated 90V (direct couple ) (0.00)
Posted by Paul Joppa on 2023-11-24, 08:23:58 (173.222.3.179)
In that case, I just size the cap for 1/gm, which is a good-enough approximation. .......
22: Tube DIY Asylum, RE: Always use a resistor load, never CCS (0.00)
Posted by Paul Joppa on 2023-10-06, 07:15:48 (73.42.214.122)
There is another way to reduce driver distortion, if that is a goal. That is, to increase the driver plate voltage so that the required peak AC output voltage is a smaller proportion of the available .......
23: Tube DIY Asylum, My experience is the opposite, but ... (0.00)
Posted by Paul Joppa on 2023-10-05, 12:47:42 (73.42.214.122)
My experience is the opposite, but there are too many extraneous factors to give a universal rule. Both conclusions are backed up by experiments, after all! .......
24: Tube DIY Asylum, VT-52 data (0.00)
Posted by Paul Joppa on 2023-09-23, 08:18:26 (73.42.214.122)
I have not seen a data sheet yet, but this site has the basics. .......
25: SET Asylum, RE: Circling back to the OP (0.00)
Posted by Paul Joppa on 2023-09-20, 22:06:29 (73.42.214.122)
tl;dr -- the choice of a driver depends on the kind of feedback used - the requirements are quite different. My view is that feedback is feedback, and UL is a form of feedback. Therefor other forms of .......
26: SET Asylum, RE: Recommend driver for SE KT88 (0.00)
Posted by Paul Joppa on 2023-09-14, 08:28:32 (73.42.214.122)
Depends on the KT88 operating point (voltages, currents, and load impedance) and on the feedback topology and amount. .......
27: MagneQuest/Peerless Forum, RE: Going though Mike's stuff anyone know what a BH5 & 6 are? (0.00)
Posted by Paul Joppa on 2023-09-11, 18:08:04 (73.42.214.122)
BH-5 is a parafeed output transformer. Basically it's a TFA-2004Jr variant, bobbin wound with Teflon layer separators, in a brass channel frame with solder tabs. Core is a 1.25-inch stack of EI87 lami .......
28: MagneQuest/Peerless Forum, RE: Going though Mike's stuff anyone know what a BH5 & 6 are? (0.00)
Posted by Paul Joppa on 2023-09-11, 15:57:08 (73.42.214.122)
Yes, those are proprietary custom designs for upgrading certain Bottlehead products. I take it there were no BH-7's? I'll dig up my notes and post some specs and history shortly. They are very nice d .......
29: Tube DIY Asylum, RE: Resistor used for measuring bias keeps failing -- what can I do? (0.00)
Posted by Paul Joppa on 2023-08-31, 22:08:11 (73.42.214.122)
There must be some other reason than normal current flow, which alone - even at maximum power - is not enough to blow a 1-watt rated resistor. A higher rated resistor wouldn't address the cause. The n .......
30: Tube DIY Asylum, RE: Sorry I posted a wrong diagram, and agai . .... (0.00)
Posted by Paul Joppa on 2023-08-26, 08:07:47 (73.42.214.122)
Yes, I agree. I see two problems with the circuit as posted: 1) the input impedance of a typical small-signal triode at zero bias is pretty low due to grid current; quite possibly less than the desire .......
31: Tube DIY Asylum, RE: Plate voltage (0.00)
Posted by Paul Joppa on 2023-08-19, 08:13:10 (73.42.214.122)
Historically, tubes were operated with their filaments in parallel - otherwise, you would need multiple large filament batteries, one for each tube. Plate voltage was derived from a "B" battery; grid .......
32: Tube DIY Asylum, Yes ... (0.00)
Posted by Paul Joppa on 2023-08-11, 14:38:53 (73.42.214.122)
... assuming the load impedance is much greater than 600 ohms. .......
33: High Efficiency Speaker Asylum, RE: How about a 12? (0.00)
Posted by Paul Joppa on 2023-08-04, 21:20:29 (73.42.214.122)
That's perfectly true, if you use an amp with a high damping factor and/or a lot of wall absorption. My interest is in SETs, which usually run a DF around 2 to 3, so I added that calculation. And you .......
34: High Efficiency Speaker Asylum, How about a 12? (0.00)
Posted by Paul Joppa on 2023-08-04, 16:37:56 (73.42.214.122)
Fostex FW305 should do 95dB in 3 cubic feet, with QT=0.5 at 50Hz, but a zero-feedback SET will bring the QT up to around 0.7. .......
35: Tube DIY Asylum, RE: Ok... (0.00)
Posted by Paul Joppa on 2023-07-28, 07:38:26 (73.42.214.122)
To get the same voltage as a red LED, you need two 1N4007s, which doubles the dynamic resistance. .......
36: Tube DIY Asylum, RE: Ok... (0.00)
Posted by Paul Joppa on 2023-07-27, 07:19:55 (73.42.214.122)
For what it's worth, some LEDs are noisier than others, though not nearly as noisy as Zeners. It matters in a phono preamp. .......
37: Tube DIY Asylum, RE: Bringing down the ripple......? (0.00)
Posted by Paul Joppa on 2023-07-18, 14:25:01 (73.42.214.122)
I have at hand data sheets for four typical rectifiers. All provide maximum ratings and typical operating conditions. Note that only the 5AR4 has a maximum capacitance rating, but all specify limiting .......
38: Tube DIY Asylum, RE: Bringing down the ripple......? (0.00)
Posted by Paul Joppa on 2023-07-13, 21:53:44 (73.42.214.122)
The resonance frequency of 1uF and 1H is 159Hz. It's a low pass above that frequency, but not at 120Hz. In fact, in this case the low pass is under-damped and has a resonance peak (about 10dB), so it .......
39: SET Asylum, RE: What kind of rectifiers were used in Don Garber's 300B mono blocks? (0.00)
Posted by Paul Joppa on 2023-06-16, 07:09:59 (73.42.214.122)
Since I don't know the circuit, component values, the actual components chosen, nor their safety margins, I can't answer either question below. The 5AR4 will result in more voltage (and power), but co .......
40: High Efficiency Speaker Asylum, RE: "resistive load that is the air." (0.00)
Posted by Paul Joppa on 2023-06-16, 06:58:32 (73.42.214.122)
About 1dB less at 6000 feet. .......
41: SET Asylum, RE: What kind of rectifiers were used in Don Garber's 300B mono blocks? (0.00)
Posted by Paul Joppa on 2023-06-15, 20:29:07 (73.42.214.122)
Seems to have been the 5AR4. Google "garber 300b" for more ... :^) .......
42: High Efficiency Speaker Asylum, RE: Raw Tannoy drivers (0.00)
Posted by Paul Joppa on 2023-05-12, 20:21:41 (73.42.214.122)
My impression has long been that HiFi was fading by the mid-sixties (as transistors replaced tubes? or stereo replaced mono?) but the hippie folk/psychedelic rock enthusiasm for music produced a tempo .......
43: SET Asylum, RE: SET Amp Sweet Spot (0.00)
Posted by Paul Joppa on 2023-05-03, 23:07:53 (172.56.169.5)
I've been exploring in the last several years the thought that there is indeed a sweet spot in the distortion signature; that is, a little bit of second harmonic improves the listening experience but .......
44: High Efficiency Speaker Asylum, RE: Autoformer and shunt resistor (0.00)
Posted by Paul Joppa on 2023-04-27, 22:08:14 (73.42.214.122)
No apologies needed; we all come to these forums to share what we know and learn what we don't. Sometimes it's hard to tell the difference. :^) .......
45: High Efficiency Speaker Asylum, RE: Autoformer and shunt resistor (0.00)
Posted by Paul Joppa on 2023-04-27, 07:34:25 (73.42.214.122)
12 dB would be a turns ratio of 4:1, which is an impedance ratio of 16:1; in other words the primary impedance with a 16 ohm load would be 256 ohms. The appropriate shunt resistance would then be 17.0 .......
46: SET Asylum, RE: I've got the Assembly Manual - Does that help ? ...............nt (0.00)
Posted by Paul Joppa on 2023-04-26, 21:13:50 (73.42.214.122)
Thanks for posting the information. I suppose Hammond has a proprietary agreement with Welborne - it's not uncommon. I believe the end bell is for EI-125 laminations, in which case you can also source .......
47: SET Asylum, RE: I've got the Assembly Manual - Does that help ? ...............nt (0.00)
Posted by Paul Joppa on 2023-04-24, 10:24:13 (73.42.214.122)
It looks very much like the Hammond 373X, except the amp needs two 6.3v windings and the 373 has only one. So it may have been a custom design. .......
48: High Efficiency Speaker Asylum, RE: Has anyone used this E-V CM12-2 12" coax in a hifi system? (0.00)
Posted by Paul Joppa on 2023-04-11, 07:45:38 (73.42.214.122)
Interesting data sheet. A ton of detailed information, but no Thiel/Small parameters. .......
49: Tube DIY Asylum, RE: Connecting headphones to SET amp (0.00)
Posted by Paul Joppa on 2023-03-25, 08:45:49 (73.42.214.122)
With zero feedback, the main effect is reduced distortion. Speakers often have much higher impedance at certain frequencies, with no problems. .......
50: Tube DIY Asylum, That's a good point (0.00)
Posted by Paul Joppa on 2023-03-05, 09:28:06 (73.42.214.122)
... although it can get expensive too. In my own designs, I have used current-sources and chokes for plate loads extensively, partly for their PSRR advantages. A choke does about as much good in the P .......
51: Tube DIY Asylum, RE: Yes Indeed! (0.00)
Posted by Paul Joppa on 2023-03-03, 22:54:37 (73.42.214.122)
I imagine Broskie himself would agree with Tre - that the simplest and most obvious solution to a PSU hum problem is a better PSU. I think he is just showing his audience how much extra trouble is nec .......
52: Tube DIY Asylum, RE: Feedback is usually misapplied. You might want to try this (0.00)
Posted by Paul Joppa on 2023-02-07, 07:20:44 (73.193.123.9)
Plate to grid feedback is also local, and is an example of what Ralph is suggesting. .......
53: High Efficiency Speaker Asylum, RE: The Curse of CCA (copper clad aluminium). I took an oath! (0.00)
Posted by Paul Joppa on 2023-02-06, 12:08:00 (73.193.123.9)
It's lighter weight, improving treble extension and/or efficiency. .......
54: High Efficiency Speaker Asylum, RE: Yes, I saw that (0.00)
Posted by Paul Joppa on 2023-01-17, 08:42:34 (73.193.123.9)
FWIW, the impedance fluctuations of a horn driver depend on the horn as much as the driver... .......
55: Tube DIY Asylum, RE: Interpretations of the various Asylums (0.00)
Posted by Paul Joppa on 2023-01-16, 21:32:15 (73.193.123.9)
Historically, I remember when TubeDIY got annoyed with the non-DIY tube posts, which were mostly SET, so the SET forum was separated out. At the time, I moved over there because this (TubeDIY) forum w .......
56: High Efficiency Speaker Asylum, RE: Are you sure about that? (0.00)
Posted by Paul Joppa on 2023-01-16, 19:05:14 (73.193.123.9)
Slagle's site shows speaker autoformers with switched resistors for each tap in parallel with the iron to maintain constant impedance. .......
57: High Efficiency Speaker Asylum, RE: Yamaha NS-30 x-over improvement? (0.00)
Posted by Paul Joppa on 2023-01-15, 07:04:58 (73.193.123.9)
Beyond replacing the 100uF midrange HP electrolytic capacitor, I don't see much that can be done. It's a very peculiar design, using bass and midrange speakers well above their piston range and in di .......
58: Tube DIY Asylum, Message sent (nt) (0.00)
Posted by Paul Joppa on 2023-01-07, 08:53:20 (73.193.123.9)
nt .......
59: Tube DIY Asylum, RE: No. UL was patented. So (0.00)
Posted by Paul Joppa on 2022-12-24, 07:30:35 (73.193.123.9)
DC method should work fine, you just have to change the screen voltage at the same time you change the plate voltage. Two high voltage supplies. If you don't have a tracking supply to make it easy, it .......
60: Tube DIY Asylum, RE: Push pulll transformer question (0.00)
Posted by Paul Joppa on 2022-12-13, 21:04:37 (73.193.123.9)
In Class A, each tube sees half the plate-to-plate impedance, in Class B each tube sees one quarter of the plate-to-plate impedance. .......
61: Tube DIY Asylum, RE: What advantages does schottky diode have when used for DHT filament (0.00)
Posted by Paul Joppa on 2022-12-13, 07:45:20 (73.193.123.9)
In addition to Chip647's post, the specific advantage of Schottky diodes for low-voltage supplies specifically is their low forward voltage drop. They are thus more efficient. That is not always usef .......
62: SET Asylum, RE: Hi B+ on Morrison Micro (moved from Tube DIY Asylum) (0.00)
Posted by Paul Joppa on 2022-12-10, 12:45:48 (73.193.123.9)
Yes indeed. Or anything that can be driven by a 45 amp. It would be interesting to compare with a 45, since they make about the same power. Another intriguing comparison would be with a 2A3 at the con .......
63: SET Asylum, RE: Recall a conversation I had with him at an audio show... (0.00)
Posted by Paul Joppa on 2022-12-10, 09:04:27 (73.193.123.9)
If my surmise(*) is correct, that means it's not suitable for use in the Micro, at 80mA current. I have not found an official maximum current for standard biplate 2A3s. .......
64: SET Asylum, RE: Hi B+ on Morrison Micro (moved from Tube DIY Asylum) (0.00)
Posted by Paul Joppa on 2022-12-09, 16:53:12 (73.193.123.9)
I agree that a "low and hot" operating point is the key to understanding the Micro circuit. Running the 2A3 at 200v and 80mA (-30v bias) seems most likely; a paralleled 6SL7 in this circuit should hav .......
65: High Efficiency Speaker Asylum, RE: Electro voice driver question (0.00)
Posted by Paul Joppa on 2022-12-03, 07:52:35 (73.193.123.9)
That might work. The crossover would need to double the capacitance. (I posted the crossover elsewhere in this long thread; here it is again.) Only the tweeter has a (switched) attenuator though. ::: .......
66: High Efficiency Speaker Asylum, RE: Electro voice driver question (0.00)
Posted by Paul Joppa on 2022-12-02, 21:30:45 (73.193.123.9)
Looks very good indeed - except it needs to be 4 ohms. There's a DCS305-4 subwoofer that's not quite as close in parameters, but IS 4 ohms. .......
67: High Efficiency Speaker Asylum, RE: Electro voice driver question (0.00)
Posted by Paul Joppa on 2022-11-30, 16:22:00 (73.193.123.9)
Here's a starting point: You should be able to get around 92dB/W efficiency at 40Hz in a 5 cubic foot box with suitable acoustic suspension drivers, which is about what you have. Assuming a Butterwort .......
68: High Efficiency Speaker Asylum, RE: Electro voice driver question - crossover (0.00)
Posted by Paul Joppa on 2022-11-30, 08:16:17 (73.193.123.9)
I found this - it's hosted on the EV web site but seems to be hidden. If accurate, many EV models were sealed boxes, and the two woofers are in series. The 8 ohm resistor in series with the midrange s .......
69: Tube DIY Asylum, Good point RE: Class B (nt) (0.00)
Posted by Paul Joppa on 2022-11-26, 07:51:38 (73.193.123.9)
It's a tradeoff between efficiency and battery life. Six decades ago (when transistors were still new) I built a transistor class A amp powered by batteries. If memory serves, a set of D-cells lasted .......
70: Tube DIY Asylum, RE: Looking for battery tube amp schematics. (0.00)
Posted by Paul Joppa on 2022-11-25, 15:08:14 (73.193.123.9)
1H6 is a voltage amp, not a power amp tube. 1H4 and 1J6 are rated primarily for Class-B push-pull power amps, which are generally not low-distortion designs. Circuit 14-8 in the RCA RC-14 tube manual .......
71: SET Asylum, RE: Frequency Response (0.00)
Posted by Paul Joppa on 2022-11-14, 14:36:26 (73.193.123.9)
When SETs first hit the American scene some 25 years ago, the conventional wisdom was deeply disturbed. It had long been accepted that the best amps had flat response, zero distortion, and zero output .......
72: SET Asylum, RE: Mastersound 300B (Vaic) (0.00)
Posted by Paul Joppa on 2022-11-10, 20:58:11 (73.193.123.9)
At 400v plate to filament, 84v bias gives 80mA; into 2500 ohms power is 12.5 watts at 3% second harmonic - all this is from the WE data sheet. That seems likeliest, given 500v power supply, cathode bi .......
73: Tube DIY Asylum, RE: Perhaps Not the Best Approach (0.00)
Posted by Paul Joppa on 2022-10-29, 15:31:01 (73.193.123.9)
If you define ideal as avoiding both premature voltage clipping and premature current clipping, then yes. There are of course many other ways to define ideal ... .......
74: SET Asylum, RE: I bet nobody here had a set amp before me ...... (0.00)
Posted by Paul Joppa on 2022-10-11, 08:59:17 (73.193.123.9)
If you count an ultralinear 6BQ5, I designed and built my first amp in 1964 (+/- a year or so). Used it with a 'Mellow Monster' back horn and Wolverine LS-8. .......
75: High Efficiency Speaker Asylum, RE: Single "fullrnge" drivers often lack high frequency extension (0.00)
Posted by Paul Joppa on 2022-09-30, 23:23:28 (173.222.3.28)
Typical large/efficient 'fullrange' drivers are much more directional at higher frequencies, so the reverberant field in the room lacks high frequency energy, even if the on-axis response is flat. Gi .......
76: Tube DIY Asylum, RE: If the wave form was a true square wave... (0.00)
Posted by Paul Joppa on 2022-09-09, 06:51:03 (76.135.237.20)
True-RMS meters have a maximum crest factor, within which they can be quite accurate. It's worth checking the specification. .......
77: High Efficiency Speaker Asylum, RE: Altec 32C (0.00)
Posted by Paul Joppa on 2022-08-05, 07:24:55 (73.42.206.223)
Fascinating - thanks for the links. FWIW, I get 89.7dB/w/m in maybe 4 cubic feet,down to 60Hz. Not nearly as efficient as I had expected. (Haven't had my coffee yet, so my arithmetic may be off...) :: .......
78: High Efficiency Speaker Asylum, RE: FWIW, I visited last week... (0.00)
Posted by Paul Joppa on 2022-08-01, 06:52:22 (172.56.104.231)
Cool! Thanks for posting - much more detail than in the NY Times. .......
79: High Efficiency Speaker Asylum, from the fashion page ... (0.00)
Posted by Paul Joppa on 2022-07-28, 14:34:18 (76.146.55.154)
New York Times today. .......
80: SET Asylum, RE: 2a3 primary choices (0.00)
Posted by Paul Joppa on 2022-07-26, 08:51:04 (76.146.55.154)
I run 2A3s at 4K, but I also revise the operating point to 300v/50mA. By my analysis, the should give similar results (power and distortion) to the spec operating point. Are you running at the usual 2 .......
81: SET Asylum, Thread at diyAudio (0.00)
Posted by Paul Joppa on 2022-07-21, 08:30:18 (76.146.55.154)
Here's a current thread at diyAudio about the Fi design. .......
82: SET Asylum, RE: What would cause filament to burn out on My 300B tubes (0.00)
Posted by Paul Joppa on 2022-07-15, 17:18:33 (76.146.55.154)
Google turned up the kit manual, which shows a 6.3v winding into a rectifier bridge and CLC filter. Hard to see any way for that to produce more than a normal voltage unless maybe the filament choke i .......
83: SET Asylum, RE: What would cause filament to burn out on My 300B tubes (0.00)
Posted by Paul Joppa on 2022-07-14, 21:01:22 (76.146.28.198)
That depends on what the filament supply looks like - i.e. we need to see a circuit diagram. .......
84: High Efficiency Speaker Asylum, RE: Ultimate 15 inch driver build. (0.00)
Posted by Paul Joppa on 2022-07-10, 07:23:19 (172.58.43.228)
True indeed. I have a pair of 22220s, both bought newly reconed by the local factory-authorized service (thus presumably re-magnetized). They have different cone masses, by about 20% IIRC. ::: TOPIC:: .......
85: Tube DIY Asylum, RE: The real problem (0.00)
Posted by Paul Joppa on 2022-06-30, 11:37:13 (76.146.28.198)
You got that right! It's a pain for everyone. The difference between instantaneous peak and short-term average listening level seems to be too complex for most people, which contributes to the confusi .......
86: Tube DIY Asylum, RE: Why not a 6SN7 with a 3K plate resistor? Pretty vertical but only 5.5db of gain (0.00)
Posted by Paul Joppa on 2022-06-29, 08:16:39 (76.146.28.198)
Draw the load line. You'll find that the power supply voltage has to drop to about 267 volts if you are to obtain 8mA at 8v bias. The maximum output becomes about 19vRMS. You can calculate the gain (5 .......
87: Tube DIY Asylum, RE: what twin triode IDH tube is the least amplification factor? I only need something like 8 (0.00)
Posted by Paul Joppa on 2022-06-25, 07:07:52 (73.11.180.136)
Lowest is probably the 6AS7/6080, mu about 2. The similar 5998 is nominally 5.5. Both are quite nonlinear, though, so the mu varies +/- 50% or so, depending on plate current and voltage. :^) ::: TOPIC .......
88: Tube DIY Asylum, RE: Fast Recovery rectifier- what does it contribute to AUDIO or for tube amp? (0.00)
Posted by Paul Joppa on 2022-06-24, 08:06:17 (73.11.180.136)
Yes, I meant without bypass components or "spike filters." .......
89: Tube DIY Asylum, RE: Fast Recovery rectifier- what does it contribute to AUDIO or for tube amp? (0.00)
Posted by Paul Joppa on 2022-06-23, 17:43:05 (73.11.180.136)
In the late nineties (IIRC) there was a flurry of interest in reverse-recovery spikes and filters t reduce them and/or reduce the high frequency ringing of the power transformer triggered by them. As .......
90: Tube DIY Asylum, RE: How can A2 happen in 845 (0.00)
Posted by Paul Joppa on 2022-06-15, 08:25:12 (73.11.180.91)
My apologies, I think I was unclear. The grid impedance is the change in GRID voltage - not the change in plate voltage - divided by the change in grid current. An admittedly extreme example: Vp=+60 V .......
91: Tube DIY Asylum, RE: How can A2 happen in 845 (0.00)
Posted by Paul Joppa on 2022-06-14, 20:43:59 (73.11.180.91)
I've done it, with a few 6DJ8/6922 tubes. Measure the grid voltage and current at multiple closely spaced points and calculate the voltage difference and current difference at adjacent points - Ohm's .......
92: SET Asylum, RE: How does 845 A2 happen, pinging NAZ or other for assistance (0.00)
Posted by Paul Joppa on 2022-06-14, 07:35:13 (73.11.180.91)
The gain is not mu unless the load impedance is infinite. Use mu*(RL/(rp+RL)) - it is the usual approximation. Or draw the load line on the plate curves. The step-up interstage transformer increases t .......
93: SET Asylum, RE: Reserve power? Problem (0.00)
Posted by Paul Joppa on 2022-06-04, 10:43:07 (73.11.180.91)
Voltages at the 300B and 5687 pins would be a good place to start. Get data from both amps and look for big differences. .......
94: SET Asylum, RE: Reserve power? Problem (0.00)
Posted by Paul Joppa on 2022-06-04, 07:53:42 (73.11.180.91)
The new distortion suggests that the operating point (voltages and currents) has been disturbed. Without a circuit diagram, it's difficult to go further. .......
95: Tube DIY Asylum, RE: Conductive plastic? (0.00)
Posted by Paul Joppa on 2022-06-03, 08:14:24 (73.11.180.91)
The specs indicate a maximum difference between channels at the midpoint of 6dB. Just sayin' ... :^) .......
96: SET Asylum, RE: Hum potentiometer Sun Audio 300b (0.00)
Posted by Paul Joppa on 2022-05-23, 08:03:58 (172.58.43.59)
Just adjust the pot for minimum hum - there should be an optimum position. It is normal to have differences between individual tubes. .......
97: Tube DIY Asylum, RE: interesting read on cap input vs choke input (0.00)
Posted by Paul Joppa on 2022-05-17, 21:08:35 (73.169.153.194)
D'oh! Thanks; of course you are right - guess I just wasn't thinking it through. .......
98: Tube DIY Asylum, RE: interesting read on cap input vs choke input (0.00)
Posted by Paul Joppa on 2022-05-17, 07:57:10 (73.169.153.194)
Interesting indeed! Thanks for posting. I wonder whether PSUD could be modified to allow for this effect? I've used PSUD to estimate the relative advantages of cap input vs. choke input filters - look .......
99: High Efficiency Speaker Asylum, RE: Can Anyone Identify This Horn ? (0.00)
Posted by Paul Joppa on 2022-05-05, 21:45:17 (73.169.153.194)
There are many possible reasons for higher crossovers; here are a few: * As you suggested, midrange power handling limitations * At high SPLs, the midrange driver may be excursion limmited and distort .......
100: High Efficiency Speaker Asylum, RE: Listed as 96db everywhere. (0.00)
Posted by Paul Joppa on 2022-05-04, 16:45:46 (73.169.153.194)
Here's a 12" that claims 97dB at f3=51Hz in 2.5 cubic feet. Sure, the sensitivity is slightly optimistic relative to the piston range - the data sheet says 2.06% half-space efficiency, which is 95dB. .......
101: High Efficiency Speaker Asylum, RE: Listed as 96db everywhere. (0.00)
Posted by Paul Joppa on 2022-05-04, 11:05:53 (73.169.153.194)
It's a 12-inch woofer in a large ported box (external dimensions are over 8 cubic feet). Even at half that internally, the claimed 50Hz bass could be achieved at close to 96dB. I agree that 96dB is un .......
102: High Efficiency Speaker Asylum, diatone on wikipedia - nt (0.00)
Posted by Paul Joppa on 2022-05-03, 11:37:24 (73.169.153.194)
nt .......
103: Tube DIY Asylum, Thanks! -nt (0.00)
Posted by Paul Joppa on 2022-04-16, 13:22:32 (73.169.153.194)
nt .......
104: Tube DIY Asylum, RE: You might be taking the wrong approach to PP; many do! (0.00)
Posted by Paul Joppa on 2022-04-14, 19:42:09 (73.169.153.194)
You said "... Karl Spangenberg and O J Schade both mention that the screen works optimally at approximately 15 ~ 20 volt below the plate ..." Do you have a reference for one or both of these? I'd like .......
105: Tube DIY Asylum, RE: I'm not interested in starting a flame war or to change your (0.00)
Posted by Paul Joppa on 2022-04-13, 07:30:23 (73.169.153.194)
That's been my experience as well. .......
106: Tube DIY Asylum, RE: Question for Tre' or (0.00)
Posted by Paul Joppa on 2022-04-02, 05:56:26 (73.169.153.194)
A CCS s usually used to linearize a (lightly-loaded) triode; but the amp is mostly pentodes, and as rage said, the one triode is a split-load phase splitter which can't use a current source. ::: TOPIC .......
107: Tube DIY Asylum, RE: Separate power supply for driver tubes in tube power amp (0.00)
Posted by Paul Joppa on 2022-03-28, 16:45:48 (73.169.153.194)
An alternative is to regulate the driver supply. Even if the driver plate load is a current source, it is an improvement (to my ears, anyhow). .......
108: Tube DIY Asylum, RE: Reading up on breakdown voltage, . . (0.00)
Posted by Paul Joppa on 2022-03-27, 08:04:34 (73.169.153.194)
There are three voltage limitations associated with resistors: The breakdown voltage is often called "dielectric strength" on data sheets. The maximum voltage end-to-end is often called working voltag .......
109: High Efficiency Speaker Asylum, Lower efficiency ... ? (0.00)
Posted by Paul Joppa on 2022-03-25, 23:03:56 (73.169.153.194)
This is the high efficiency asylum, so most have not questioned the 100dB spec. But you did say looks were more important than sound, so you should probably consider lower-efficiency options. 300B am .......
110: Tube DIY Asylum, RE: TV Damper Diode in Bridge - elevate heater or not? (0.00)
Posted by Paul Joppa on 2022-03-23, 11:37:50 (73.169.153.194)
Don't do that - the lowest diode voltage is at ground, so you'd have the cathode 400v negative fr0m the heater, which violates the other asymmetric limit. .......
111: Tube DIY Asylum, RE: TV Damper Diode in Bridge - elevate heater or not? (0.00)
Posted by Paul Joppa on 2022-03-23, 08:24:28 (73.169.153.194)
1) The peak positive voltage occurs when the diodes are conducting, so plate voltage equals cathode voltage +/- a tiny amount. If there is no load (tube not warmed up or missing) it will be the square .......
112: Tube DIY Asylum, Thank you! (0.00)
Posted by Paul Joppa on 2022-03-18, 10:37:00 (73.169.153.194)
That's the article I was thinking of. .......
113: Tube DIY Asylum, Apologies - yu are right - RE: 2a3 amp (0.00)
Posted by Paul Joppa on 2022-03-17, 09:03:19 (73.169.153.194)
Yes, my math was off. The corner frequency is 1/(2*pi*rp*C), giving 20kHz. I really should not post so late at night! I'll edit my post. .......
114: Tube DIY Asylum, RE: 2a3 amp (0.00)
Posted by Paul Joppa on 2022-03-16, 20:39:37 (73.169.153.194)
I put together some numbers, in the hope that it will help focus this discussion: The high frequency -3dB point is at [edit: original expression rp*C/(2*pi) was wrong, should be 1/(2*PI*rp*C)], where .......
115: High Efficiency Speaker Asylum, RE: EV EQ (0.00)
Posted by Paul Joppa on 2022-02-15, 18:04:21 (73.169.153.194)
Does your preamp not have a tape monitor loop? Normally, the tape recorder goes between the source selector and the level control, so the signal is always at line level, independent of the volume set .......
116: SET Asylum, RE: The Ultimate 2A3 SET amp (0.00)
Posted by Paul Joppa on 2022-02-12, 21:17:50 (73.169.153.194)
As TK says, there are too many ways to make a great 2A3 amp. It's like trying to write the ultimate poem, using the best of the best words. Where do you start? But you also asked for suggestions, so I .......
117: Tube DIY Asylum, RE: Please explain........? (0.00)
Posted by Paul Joppa on 2022-02-09, 09:44:45 (73.169.153.194)
What TK and I are saying is that the current meters are not perfect; they do not have zero resistance between the two terminals. I'll add that the battery is not perfect either; its voltage will chang .......
118: Tube DIY Asylum, RE: Please explain........? (0.00)
Posted by Paul Joppa on 2022-02-08, 20:36:56 (73.169.153.194)
To calculate the current, you must add the meter's resistance to the 21.1 ohm resistor. .......
119: Tube DIY Asylum, RE: Looking for Other Low Wattage SE OPT Options (0.00)
Posted by Paul Joppa on 2022-02-02, 20:11:48 (73.169.153.194)
Vintage transformers since the fifties are mostly push-pull, and older transformers have inferior core materials. .......
120: SET Asylum, Sound advice, IMHO (0.00)
Posted by Paul Joppa on 2022-01-27, 06:49:19 (73.169.153.194)
Separate phono preamps and power amps can be hidden away, since they don't have any controls beyond power switches. Many people like to put the power amp near the speakers, for example. Preamps are so .......
121: Tube DIY Asylum, RE: Need Help Shhh-ing my Thorsten Mods EAR 834P (0.00)
Posted by Paul Joppa on 2022-01-26, 14:15:53 (73.169.153.194)
What is the output of the cartridge? MM or MC? .......
122: Tube DIY Asylum, RE: The AZ11 is directly heated, does that make a difference? (0.00)
Posted by Paul Joppa on 2022-01-20, 06:38:11 (73.169.153.194)
Yes, it could make a difference, assuming the two filaments are identical and in parallel. The effective peak voltage when one diode is conducting will be slightly higher than the other, adding some f .......
123: SET Asylum, RE: How often do you roll? (0.00)
Posted by Paul Joppa on 2022-01-08, 07:29:42 (73.169.153.194)
Some tubes DO need broken in. The issue is called "forming the cathode." It's the final step in making a tube - the cathode is heated, usually a bit hotter than nominal operating temperature, and some .......
124: High Efficiency Speaker Asylum, RE: It's called "doping" (0.00)
Posted by Paul Joppa on 2022-01-05, 09:08:35 (73.169.153.194)
Ideally, I believe, it's also used to damp the "rim resonance" which can sometimes be seen in the response or and/or the impedance plots, usually at a few hundred Hz. .......
125: Tube DIY Asylum, RE: Now this is weird (0.00)
Posted by Paul Joppa on 2022-01-04, 20:05:41 (73.169.153.194)
Sounds like you have some iffy socket/tube pin connections or dirty tube pins. It's good practice to isolate the transformer frames and ground them to the (single) safety/chassis ground point. ::: TOP .......
126: Tube DIY Asylum, RE: What would be the sonic effect for this Audionote line stage (0.00)
Posted by Paul Joppa on 2022-01-04, 08:07:48 (73.169.153.194)
The low load resistance increases distortion, the unbypassed cathode resistor reduces distortion. But the large headroom in this first stage reduces the distortion by a very large margin, so it doesn' .......
127: Tube DIY Asylum, RE: What would be the sonic effect for this Audionote line stage (0.00)
Posted by Paul Joppa on 2022-01-03, 12:04:21 (73.169.153.194)
Like Triode_Kingdom, I should not post before coffee ... :^) As calculated by the OP, the effective rp is about 20K for a single triode with unbypassed Rk. Two in parallel is 10K. The plate load resis .......
128: Tube DIY Asylum, RE: What would be the sonic effect for this Audionote line stage (0.00)
Posted by Paul Joppa on 2022-01-03, 08:34:03 (73.169.153.194)
The plate resistance is paralleled with the load resistance to get the output resistance, so something like 6K ohms output resistance - can easily drive the 100K load. The operating point is fairly "l .......
129: Tube DIY Asylum, RE: Current reading different accross choke and resistor??? (0.00)
Posted by Paul Joppa on 2021-12-26, 20:22:29 (73.169.153.194)
Voltage across a power supply choke likely includes AC as well as DC components. .......
130: MagneQuest/Peerless Forum, RE: FS-100 Output Wiring (0.00)
Posted by Paul Joppa on 2021-12-24, 12:08:13 (73.169.153.194)
Yes, I know the winding details. (I consulted with Mike when he was developing the parafeed version. It's surprisingly sophisticated...) As far as I know, the details are still proprietary, but effect .......
131: MagneQuest/Peerless Forum, RE: FS-100 Output Wiring (0.00)
Posted by Paul Joppa on 2021-12-23, 18:28:08 (73.169.153.194)
I believe that black to brown is always 4 ohms. .......
132: Tube DIY Asylum, RE: 100k input resistor ??? (0.00)
Posted by Paul Joppa on 2021-12-23, 10:57:34 (73.169.153.194)
A one-to-one impedance ratio is most efficient on a power-transmitted basis, but on a voltage basis it loses 6dB (half the voltage). Ten-to-one loses a bit less than 1dB, which I suspect is the origin .......
133: Tube DIY Asylum, RE: This circuit appears capable of that voltage swing. (0.00)
Posted by Paul Joppa on 2021-12-22, 15:35:25 (73.169.153.194)
My remarks on plate load were intended as an alternative to an unbypassed cathode resistance - sorry I wasn't clear on that. For the feedback, I estimated the voltages and currents based on the resist .......
134: Tube DIY Asylum, RE: This circuit appears capable of that voltage swing. (0.00)
Posted by Paul Joppa on 2021-12-22, 08:21:32 (73.169.153.194)
A quick estimate is that the negative feedback is only 3dB, so it's not what I would call "significant", though quite possibly audible. The other way to reduce driver distortion is to use a high plate .......
135: Tube DIY Asylum, RE: 6hb5 compactron test (0.00)
Posted by Paul Joppa on 2021-12-20, 15:22:53 (73.169.153.194)
" ... compactron are not able to be tested accurately ... " And does Andy say that other similar tubes in octal envelopes can be accurately tested out of circuit? Of course, many older testers don't h .......
136: MagneQuest/Peerless Forum, RE: Altec 17173 Choke Specifications (0.00)
Posted by Paul Joppa on 2021-12-15, 16:24:21 (73.169.153.194)
I have two notes in my files, from conversations with Mike: "Original Peerless was two identical bays, nominally 5K/20K". "17173 is nominally 5K/20Kct; the original was two bays, not reverse wound." ( .......
137: SET Asylum, RE: Can I get by with 2 watts? Used my Dbs meter (0.00)
Posted by Paul Joppa on 2021-12-13, 14:37:57 (73.169.153.194)
The main difficulty is that the short-term average sound level (which is measured by sound level meters and VU meters) is much lower than the instantaneous peaks. This difference is called headroom, a .......
138: SET Asylum, RE: Can I get by with 2 watts? (0.00)
Posted by Paul Joppa on 2021-12-09, 15:14:10 (73.169.153.194)
Two watts is about 5dB less than 6.5 watts, so the 96-97deB speakers with 2 watts will be about 5dB louder than the Daytons with 6.5 watts. For what it's worth. .......
139: Tube DIY Asylum, RE: So the Crown input sensitivity is pretty low (0.00)
Posted by Paul Joppa on 2021-12-08, 21:38:38 (73.169.153.194)
I don't think the dB reduction would be very much - the first stage is run very "low and hot" from a high supply voltage, so R3 is 50-100 times R2 - not much feedback. .......
140: Tube DIY Asylum, RE: Cathode Stripping (0.00)
Posted by Paul Joppa on 2021-12-07, 16:29:31 (73.169.153.194)
Terman (Radio Engiineering 3rd edition, 1947 p.187) says: "With thoriated tungsten cathodes, the bombardment by positive ions tends to strip off the emitting surface layer of thorium. Tubes using thor .......
141: Tube DIY Asylum, RE: How to Reduce Signal from Pre-Amp to Amps ............... (0.00)
Posted by Paul Joppa on 2021-12-07, 15:57:06 (73.169.153.194)
That will work too. It just adds another box and set of interconnects; if that's not an issue (or if it's an advantage?) then no problem. .......
142: Tube DIY Asylum, RE: How to Reduce Signal from Pre-Amp to Amps ............... (0.00)
Posted by Paul Joppa on 2021-12-07, 05:34:30 (73.169.153.194)
Neither Rothwell nor Harrison admit to their actual impedances. IIRC Rothwell in the past claimed 100K input impedance, but the information on their site now (max source impedance = minimum load imped .......
143: Tube DIY Asylum, RE: How to Reduce Signal from Pre-Amp to Amps ............... (0.00)
Posted by Paul Joppa on 2021-12-06, 12:24:48 (73.169.153.194)
Harrison Labs makes in-line attenuators of up to 12dB. Parts Express, among others, sells them. .......
144: Tube DIY Asylum, RE: Cathode Stripping (0.00)
Posted by Paul Joppa on 2021-12-01, 18:31:31 (73.169.153.194)
The terms for cathode damage are used very inconsistently. As I understand it, there are three kinds: 1) Poisoning happens when a cathode is bombarded by positive ions, which chemically bond to the su .......
145: Tube DIY Asylum, RE: Same Question to yourself .............. (0.00)
Posted by Paul Joppa on 2021-11-16, 21:10:22 (73.169.153.194)
700W bridged into 8 ohms is exactly 2 times 350 watts into 4 ohms. Tre' is right, the power supply limits the 4-ohm (unbridged) to 350 watts, less than twice the 8-ohm (unbridged) which would otherwi .......
146: Tube DIY Asylum, RE: Marketing (0.00)
Posted by Paul Joppa on 2021-11-16, 16:58:18 (73.169.153.194)
When a stereo amp is "bridged", that usually means the outputs are in series, so the available voltage is doubled. If the speaker impedance is the same, then it will draw twice the current as well, gi .......
147: High Efficiency Speaker Asylum, + another 1 (0.00)
Posted by Paul Joppa on 2021-11-05, 15:23:10 (73.169.153.194)
I also agree that SET amps need some headroom to sound their best, especially with spectrally dense material (orchestral, big band, etc). I'm using JBL 2220 woofers at 101dB with 8-watt 300B amps. ::: .......
148: SET Asylum, RE: 6N1P (0.00)
Posted by Paul Joppa on 2021-11-05, 08:33:29 (73.169.153.194)
".... The only Russian substitute that I know works in his gear is the 6N23P...... (Although I don't like them in the line stage. I like Philips 6DJ8s in his line stage.) ...." The 6N1P is a fine soun .......
149: Tube DIY Asylum, RE: How much current needed for a 6SN7 preamp? (0.00)
Posted by Paul Joppa on 2021-11-04, 08:20:57 (73.169.153.194)
Depends on the circuit and on the voltages. I can easily see anything from 15mA/150v to 40mA/525v, depending on design choices. .......
150: High Efficiency Speaker Asylum, RE: dumb questions. High / low efficiency threshold? (0.00)
Posted by Paul Joppa on 2021-11-02, 11:26:54 (73.169.153.194)
This was discussed here several years ago; it comes up again every now and then. My own opinion is that 96dB/watt/meter marks the boundary. That is enough for "most audiophiles, most of the time" when .......
151: Tube DIY Asylum, RE: batteries, anyone? (0.00)
Posted by Paul Joppa on 2021-10-31, 00:32:01 (73.169.153.194)
When they first arrived, I seem to remember the Chinese-made Duracells acquired a bad reputation. But they were cheaper! ... Personally, I think it's idiot Marketing types, or greedy Corporate types, .......
152: High Efficiency Speaker Asylum, RE: SAP Quartette impedence? (0.00)
Posted by Paul Joppa on 2021-10-30, 22:56:45 (73.169.153.194)
There is very little information on the web, but I see that the midrange has no crossover components - it's across the full-range signal. So I'll speculate the woofer is in parallel and both are 8 ohm .......
153: SET Asylum, RE: 300B - Is this thermal runaway ? (0.00)
Posted by Paul Joppa on 2021-10-29, 16:59:33 (73.169.153.194)
As you have tried 3 different caps, that seems unlikely to be the problem. But the grid is being raised 275v above ground, and there must be a reason. Several candidate reasons (oscillation, open grid .......
154: SET Asylum, RE: 300B - Is this thermal runaway ? (0.00)
Posted by Paul Joppa on 2021-10-28, 13:10:41 (73.169.153.194)
A few ideas re: "300B grid to ground goes up to almost 275 VDC and the Cathode voltage similarly climbs to about 120 VDC before I switch off." If this is accurate, it seems likely the grid resistor is .......
155: High Efficiency Speaker Asylum, RE: Questions About Bi Amping With Electronic Crossover (0.00)
Posted by Paul Joppa on 2021-10-18, 09:27:13 (73.169.153.194)
The crossover linked in the initial post appears to be a standard biquad filter, with no sign of phase reversal internally. In practice, the phase reversal recommendation assumes that the drivers are .......
156: Tube DIY Asylum, RE: Any insight into how the Jolida Black Ice "dimensionality" circuit works? (0.00)
Posted by Paul Joppa on 2021-10-14, 18:51:21 (73.169.153.194)
I really have no idea :^) Both amps should have very similar distortion signatures; the main differences being that one has the 3B7 and the other has direct coupling. .......
157: Tube DIY Asylum, RE: Any insight into how the Jolida Black Ice "dimensionality" circuit works? (0.00)
Posted by Paul Joppa on 2021-10-14, 14:50:22 (73.169.153.194)
They don't say much about it, but I'll speculate anyhow: 1) The 12AU7 input buffer probably provides a bit of second harmonic, which has some effect on imaging among other things. (Changing the load i .......
158: SET Asylum, RE: Book operating point seems to sound very good (0.00)
Posted by Paul Joppa on 2021-10-13, 08:01:44 (73.169.153.194)
I've said this before - you can't speak of operating point without including the load impedance. For example, the book operating point is 250v/60mA/2500 ohms and has very similar distortion, damping f .......
159: SET Asylum, RE: Tube matching in SET amplifiers (0.00)
Posted by Paul Joppa on 2021-10-02, 22:42:30 (172.58.45.51)
Craftsman style was always into copper ... .......
160: SET Asylum, Thanks! (0.00)
Posted by Paul Joppa on 2021-09-29, 08:38:56 (73.169.153.194)
...for the link and info. Very imaginative and creative design! .......
161: High Efficiency Speaker Asylum, RE: Stoopid question. I know, but... (0.00)
Posted by Paul Joppa on 2021-09-27, 16:01:51 (73.169.153.194)
You might ask Tekton if they can be successfully re-painted, or if they have any other ideas. .......
162: Tube DIY Asylum, RE: It's a No-Go (0.00)
Posted by Paul Joppa on 2021-09-21, 08:24:24 (73.169.153.194)
Yes, the regulator must be able to supply the peak screen current at full power, which can be much greater than the average current. Capacitors store energy, shunt regulators do not. Series regulators .......
163: SET Asylum, RE: Budget speakers to pair with SET amp (0.00)
Posted by Paul Joppa on 2021-09-17, 17:44:29 (73.169.153.194)
It would indeed be interesting to see what a video designer would come up with for an SET! .......
164: SET Asylum, RE: Budget speakers to pair with SET amp (0.00)
Posted by Paul Joppa on 2021-09-17, 08:24:30 (73.169.153.194)
There are two resistances to consider - the source impedance and the intended load (speaker) impedance. Most amps are designed around 4, 8, and/or 16 ohm loads, but the source impedance depends on the .......
165: SET Asylum, RE: Here's one from left field... (0.00)
Posted by Paul Joppa on 2021-09-16, 20:42:09 (73.169.153.194)
A small correction - the Stereomour 2A3 puts out 3.5 watts; it's the Kaiju 300B that puts out 8+ watts. .......
166: Tube DIY Asylum, RE: Losses in Output Transformers (0.00)
Posted by Paul Joppa on 2021-09-16, 18:01:00 (73.169.153.194)
I have, more than once(!), found that my gut feel for "close enough" is not always in fact close enough, and I have to start over with more attention to more details. In the initial post, you drew at .......
167: Tube DIY Asylum, RE: Losses in Output Transformers (0.00)
Posted by Paul Joppa on 2021-09-15, 21:49:09 (73.169.153.194)
Taking as an example the Dyna A470, the end-to-end DC resistance of the primary is about 200 ohms. Usually the secondary losses are equal to the primary losses, so total about 400 ohms. The reflected .......
168: Tube DIY Asylum, RE: dynaclone and triode not offering transformers (0.00)
Posted by Paul Joppa on 2021-09-08, 14:05:43 (73.169.153.194)
I have a pair of "A470"s, bought from Triode more than 20 years ago; I just now measured the turns ratios and got: 4 ohm tap: 4190 ohms anode-anode 8 ohm tap: 4676 --- " --- 16 ohm tap: 4306 --- " --- .......
169: Tube DIY Asylum, RE: dynaclone and triode not offering transformers (0.00)
Posted by Paul Joppa on 2021-09-06, 18:21:51 (73.169.153.194)
re "John Atwood tested the Z565 at 9.5K." According to the usual sources, it's 8K. I see that he also says the A470 is 5.6K ohms; the usual sources say 4.3K. I have some doubts about these measurement .......
170: Tube DIY Asylum, RE: Quick fix to drop power supply volts (0.00)
Posted by Paul Joppa on 2021-08-24, 19:06:12 (73.169.153.194)
The main risk is that a series Zener will not change the voltage fluctuations that might be caused by either mains voltage fluctuations or by push-pull current demand fluctuations. Since the total vol .......
171: Tube DIY Asylum, RE: Problem with Small Hammond Transformers and Chokes (0.00)
Posted by Paul Joppa on 2021-08-18, 20:42:45 (73.169.153.194)
Fiber step washers provide electrical isolation as well as elevation, and you can still tighten the screws. It's a good idea anyhow to isolate the frames and ground each to a star safety ground - reso .......
172: Tube DIY Asylum, RE: 6H30 (1/2) vs 6GK5 in linestage (0.00)
Posted by Paul Joppa on 2021-08-17, 08:42:34 (172.58.46.212)
"I have 6SN7 Aikido now. Would you suggest a 6H30 with output transformer a true upgrade?" They are very different circuits; sufficiently different that I would not care to make a prediction. Both are .......
173: Tube DIY Asylum, RE: 6H30 (1/2) vs 6GK5 in linestage (0.00)
Posted by Paul Joppa on 2021-08-15, 23:19:54 (172.58.43.252)
6GK5 is less linear than 6H30, and the 30K transformer needs more than twice the signal voltage compared to 6K. Both of those increase distortion. I prefer minimal distortion in a line-level stage, so .......
174: Tube DIY Asylum, RE: un-documented P-P OPT secondary wiring question (0.00)
Posted by Paul Joppa on 2021-08-12, 13:58:23 (73.169.153.194)
You can only parallel windings that have the same number of turns, and the impedance ratio of the transformer is not changed when you do that. So Zparallel = Za = Zb .......
175: Tube DIY Asylum, RE: un-documented P-P OPT secondary wiring question (0.00)
Posted by Paul Joppa on 2021-08-11, 21:31:53 (73.169.153.194)
Your formula for series connection has the square and square-root reversed. Impedance is proportional to the turns squared, so the number of turns is proportional to the square root of the impedance. .......
176: High Efficiency Speaker Asylum, RE: Hit or Miss (0.00)
Posted by Paul Joppa on 2021-08-06, 21:16:58 (73.169.153.194)
A friend of mine with some club-systems experience is occasionally asked to adjust the system. He just sets all the knobs to flat, and it almost always makes a big improvement. :^) .......
177: High Efficiency Speaker Asylum, RE: Changing EdgarHorn D130 from 16ohm to 8ohm? (0.00)
Posted by Paul Joppa on 2021-07-28, 21:14:02 (73.169.153.194)
Be aware that some very early JBL drivers were labelled 16 ohms but had a 6-7 ohm voice coil. IIRC, the 130A and D130 were among them, and the N1200 network did not change but was re-rated from 16 to .......
178: Tube DIY Asylum, RE: Bottlehead c4s w/standard RED LED's (0.00)
Posted by Paul Joppa on 2021-07-22, 08:08:09 (73.169.153.194)
That's the true story, except it was a 6DN7, not a 6BQ5. .......
179: Tube DIY Asylum, RE: Bottlehead c4s (0.00)
Posted by Paul Joppa on 2021-07-21, 18:32:13 (73.169.153.194)
That's the one we use. The data sheet I have is from Agilent, Mouser lists them as made by Broadcom, DigiKey says Avago - I have no idea whether all these names have their own factories or are the sam .......
180: Tube DIY Asylum, RE: Bottlehead c4s (0.00)
Posted by Paul Joppa on 2021-07-21, 13:28:36 (73.169.153.194)
The original HP LEDs have been out of production for many years. We currently use a version with identical performance specifications but a different format. The originals were chosen by the late John .......
181: Tube DIY Asylum, RE: Bottlehead c4s (0.00)
Posted by Paul Joppa on 2021-07-21, 13:14:04 (73.169.153.194)
FWIW those appear to be the oldest version, from some 20 years ago. The LEDs would have been the original HP version. .......
182: Tube DIY Asylum, RE: The circuit as drawn won't work. But (0.00)
Posted by Paul Joppa on 2021-07-13, 18:56:59 (73.169.153.194)
If you just set one of the plate resistors to zero, the DC operating points will become grossly unbalanced, since the plate to cathode voltage is much different. Substitute a zener for one resistor, o .......
183: Tube DIY Asylum, RE: balanced input, SE output, common mode rejection (0.00)
Posted by Paul Joppa on 2021-07-06, 14:47:59 (73.169.153.194)
Common-mode noise will show up across the cathode resistor of the long-tailed pair, and therefor across the plate load resistors. So the cathode resistance should be as high as possible - a current so .......
184: Tube DIY Asylum, RE: Ahh, so it does, Tre', and I missed it (0.00)
Posted by Paul Joppa on 2021-07-03, 18:34:19 (73.169.153.194)
I believe max working voltage is the same thing as limiting element voltage. Both are ways to avoid saying "rated voltage", because the rated voltage depends also on power and resistance as well - as .......
185: Tube DIY Asylum, RE: "should be all that's required" (0.00)
Posted by Paul Joppa on 2021-06-25, 22:31:54 (73.169.153.194)
If you use an LED in place of the three diodes, it should flash when that condition exists, right? :^) I think orange or amber would be about 1.8 volts. .......
186: Tube DIY Asylum, RE: I know that (0.00)
Posted by Paul Joppa on 2021-06-25, 22:26:18 (73.169.153.194)
Radio Shack goes back to 1920, supporting ham radio at first. They entered the high fidelity field in 1939. Realistic goes back to 1954 (Realist at first, but Stereo Realist sued for copyright infring .......
187: Tube DIY Asylum, RE: Because tubes rule! (0.00)
Posted by Paul Joppa on 2021-06-24, 19:24:11 (73.169.153.194)
I visited the local store in Seattle often, in the early sixties when I was a teenager. .......
188: Tube DIY Asylum, RE: Not sure it's an EICO HF-14 schematic... (0.00)
Posted by Paul Joppa on 2021-06-23, 09:41:04 (73.169.153.194)
The voltages in that manual look much more plausible (except for the missing OPT center tap!). The also match the HF81 voltages. I'll accept the theory that SAMs got it wrong. .......
189: Tube DIY Asylum, The HF-81 looks much better, but ... (0.00)
Posted by Paul Joppa on 2021-06-22, 17:03:23 (73.169.153.194)
... the original post said he was building an HF-14, and provided a different circuit. .......
190: Tube DIY Asylum, High G2 voltage (0.00)
Posted by Paul Joppa on 2021-06-22, 14:15:30 (73.169.153.194)
I couldn't help but notice in the schematic the unusually high 60 volt drop on each side of the output transformer, and the resulting 375v on the screen - 75v above the rated maximum and quiescent G2 .......
191: SET Asylum, RE: Something New Under the Sun? (0.00)
Posted by Paul Joppa on 2021-06-12, 13:38:07 (73.169.153.194)
Fortunately for us, John Broskie dug up the patent and analyzed it. Basically it's a dissimilar push-pull with one MOSFET and one triode. .......
192: Tube DIY Asylum, RE: Transformers buzzing (RCA 203 SE 6BQ5 amp and VPI PLC speed controller) (0.00)
Posted by Paul Joppa on 2021-06-05, 07:54:43 (73.169.153.194)
Sometimes excessive power line voltage will cause mechanical buzzing, especially in older equipment designed for voltages less than the current standard of 120v. .......
193: Tube DIY Asylum, +1 /nt (0.00)
Posted by Paul Joppa on 2021-06-04, 08:01:13 (73.169.153.194)
nt .......
194: Tube DIY Asylum, RE: But my expectation was that the first amp was going to sound great... (0.00)
Posted by Paul Joppa on 2021-06-02, 09:12:26 (73.169.153.194)
I have had the experience, not often but more than once, of hearing someone else's amplifier without knowing its history, and recognizing the sound as that of new capacitors. On being asked, the owner .......
195: Tube DIY Asylum, RE: Cathode bypass... (0.00)
Posted by Paul Joppa on 2021-05-31, 16:59:24 (73.169.153.194)
It does increase the variability, so you need a bit more voltage headroom unless you can the bias periodically. The problem is even greater using current-source plate loads (which force a constant bia .......
196: Tube DIY Asylum, RE: Capacitor break-in (0.00)
Posted by Paul Joppa on 2021-05-31, 11:44:08 (73.169.153.194)
If you ever find a good answer to that question, please share! I've had the same experience, repeatedly, with interstage and parafeed capacitors and with output transformers. None of the candidate th .......
197: Tube DIY Asylum, RE: Surprised you guys haven't tried it.... (0.00)
Posted by Paul Joppa on 2021-05-24, 10:03:49 (73.169.153.194)
I'm a little surprised myself, actually. We've stuck with shunt regulation, which goes all the way to DC,but the idea of a very long time constant has its attractions. .......
198: Tube DIY Asylum, RE: FET ripple filters (0.00)
Posted by Paul Joppa on 2021-05-23, 22:03:09 (73.169.153.194)
The output signal current loop, at least in series feed, includes the power supply, so if MOSFETs are audible when used as source followers, then they may well have the same effect as power supply out .......
199: Tube DIY Asylum, RE: EF86 SPICE (0.00)
Posted by Paul Joppa on 2021-05-20, 07:50:53 (73.169.153.194)
3% distortion at large signal levels seems pretty good to me. You can linearize it with local feedback (unbypassed cathode resistor), at the price of reduced transconductance, or you can give up direc .......
200: SET Asylum, RE: Here you go ........ (0.00)
Posted by Paul Joppa on 2021-05-18, 08:29:36 (73.169.153.194)
Thanks! Hashimoto H-20-3.5U; details easily found on the web. I was very interested to see that a 3.5K primary is being used, as opposed to the 4.8K of the UBT-2. The best 45 amp I've heard happened .......
201: SET Asylum, RE: the schematic ... (0.00)
Posted by Paul Joppa on 2021-05-17, 20:55:18 (73.169.153.194)
Interesting. Hashimoto is certainly a good name - do you have a model number or link? I'm always interested in good-sounding transformers and what characteristics might be associated with the sound. .......
202: SET Asylum, RE: the schematic ... (0.00)
Posted by Paul Joppa on 2021-05-17, 18:02:31 (73.169.153.194)
I'll speculate that the choice of output transformer plays a large role. That UBT-2 (apparently no longer available) has huge magnetic headroom when used with a 45. .......
203: Tube DIY Asylum, RE: WTH are you talking about? (0.00)
Posted by Paul Joppa on 2021-05-17, 09:09:22 (73.169.153.194)
Looking at the photograph in the Amazon link, that appears to be the case for the far-left (smallest) bit. .......
204: Tube DIY Asylum, RE: The Details (0.00)
Posted by Paul Joppa on 2021-05-13, 20:17:54 (73.169.153.194)
I agree with Triode Kingdom, 3.5K is a very reasonable load for the Stereomour circuit. In fact, we've used 3K with quite good results. If you decide to go that way, post on the Bottlehead forum and w .......
205: Tube DIY Asylum, RE: What value OPT does the SEX use? (0.00)
Posted by Paul Joppa on 2021-05-13, 12:03:19 (73.169.153.194)
The Bottlehead S.E.X. amp uses a transformer of 8000 ohms primary impedance. (The same transformer is also used at a 4K primary impedance in a 2A3 amp.) .......
206: Tubes Asylum, RE: How important is tube matching (0.00)
Posted by Paul Joppa on 2021-05-12, 17:40:36 (73.169.153.194)
So each monobloc has two sets of three tubes in parallel (for a total of six tubes). To maintain current balance, the total transconductance of each trio should be the same, which you could do by usi .......
207: Tubes Asylum, RE: How important is tube matching (0.00)
Posted by Paul Joppa on 2021-05-12, 13:53:13 (73.169.153.194)
It's generallymore important within an amp that between amps. Are the amps push-pull? Are the tubes in pentode mode? Ultralinear? Triode-wired? Do they have negative feedback? It makes a difference. : .......
208: Tube DIY Asylum, RE: Ground Network (0.00)
Posted by Paul Joppa on 2021-05-06, 16:04:53 (73.169.153.194)
It's not a substitute for a star ground scheme, but rather how the ground scheme (star or otherwise) is connected to the chassis. .......
209: Tube DIY Asylum, RE: Safety Last (0.00)
Posted by Paul Joppa on 2021-05-05, 17:10:56 (73.169.153.194)
There is a subtlety missing here. Properly done, the safety ground is still bonded to the chassis; only the signal ground is lifted. If line voltage shorts to chassis, the lift circuit is not involved .......
210: Tube DIY Asylum, Distortion RE: Increasing Gain in Respectable Transconductance 7 Pin Mini Types (0.00)
Posted by Paul Joppa on 2021-05-04, 07:47:35 (73.169.153.194)
Those appear to be significantly less linear than the 6BN4 - probably OK in a cathode follower or cathodyne splitter as long as the quiescent current is high enough. .......
211: Tube DIY Asylum, RE: LCR Phono stage (0.00)
Posted by Paul Joppa on 2021-04-25, 22:29:25 (73.169.153.194)
I seem to recall that someone made a 10Kohm version of the filter - I don't know if it's still available. At 600 ohms, there are a few triodes capable of a 600 ohm plate resistance, if you wish to avo .......
212: Tube DIY Asylum, RE: Can someone explain this phase inverter circuit to me? (0.00)
Posted by Paul Joppa on 2021-04-24, 21:19:23 (73.169.153.194)
The inverted (second) stage is in series with the first stage so it has both rolloffs; the second rolloff is much lower in frequency so it has minimal difference. .......
213: Tube DIY Asylum, RE: Can someone explain this phase inverter circuit to me? (0.00)
Posted by Paul Joppa on 2021-04-24, 16:42:23 (73.169.153.194)
The loads on the inverter plates (i.e. the EL84 grid resistors) are also different. It's not a symmetrical inverter, so there's no reason to expect symmetrical component values. .......
214: Tube DIY Asylum, RE: Inspiration (0.00)
Posted by Paul Joppa on 2021-04-22, 16:58:07 (73.169.153.194)
Stippich is his name. Josh Stippich. Amazingly good metal sculptor. .......
215: Tube DIY Asylum, RE: Standby/Operate Switch on my Cary Super Amplifier (AE-25) (0.00)
Posted by Paul Joppa on 2021-04-12, 11:58:21 (73.169.153.194)
Oh, I just meant using the standby for short periods before and after applying high voltage. .......
216: Tube DIY Asylum, RE: Littelfuse 5582? (0.00)
Posted by Paul Joppa on 2021-04-12, 11:51:05 (73.169.153.194)
John "Buddha" Camille used to advocate vacuum switches to avoid arcing when switching high DC voltages. .......
217: Tube DIY Asylum, RE: Standby/Operate Switch on my Cary Super Amplifier (AE-25) (0.00)
Posted by Paul Joppa on 2021-04-12, 11:34:16 (73.169.153.194)
Yes, interface resistance is a risk of long-time operation without HV current. In compensation, correct use of the standby switch reduces cathode stripping, extending the life. There are many other si .......
218: Tube DIY Asylum, RE: Littelfuse 5582? (0.00)
Posted by Paul Joppa on 2021-04-12, 11:25:09 (73.169.153.194)
You would have to do the analysis to answer that. I have not done it, I'm just reporting "conventional wisdom" on the subject. As I recall, a 15-amp rating was said to be common in guitar amps. YMMV. .......
219: Tube DIY Asylum, RE: Standby/Operate Switch on my Cary Super Amplifier (AE-25) (0.00)
Posted by Paul Joppa on 2021-04-12, 08:52:14 (73.169.153.194)
It blocks the return current from the rectifier/filter to the transformer, if that helps. The tube heaters still work, but with no HV current, no output is produced. The tubes are not as hot, and the .......
220: Tube DIY Asylum, RE: FS-100 (0.00)
Posted by Paul Joppa on 2021-04-09, 17:16:43 (73.169.153.194)
Thanks for the spec sheet - I'm adding it to my files :^) With respect to the power handling, my calculations show 30 watts at 40Hz, following Mike's design rules as I understand them. With respect t .......
221: Tube DIY Asylum, RE: 38H OPT for 845, so so? (0.00)
Posted by Paul Joppa on 2021-04-09, 12:27:40 (73.169.153.194)
Probably more like 16 pounds for the FS-100. I don't have the specs, but a quick estimate is in the range of 40-60 henries at 100mA. (I have some proprietary information to base this on.) Since mass i .......
222: Tube DIY Asylum, RE: 38H OPT for 845, so so? (0.00)
Posted by Paul Joppa on 2021-04-08, 08:47:34 (73.169.153.194)
It would be typical of good 300B amplifiers (and will weigh about twice as much as 38 henries,for the same DC current capacity). Such transformers (30 watts at 10K ohms) are quite rare in the market b .......
223: Tube DIY Asylum, RE: 38H OPT for 845, so so? (0.00)
Posted by Paul Joppa on 2021-04-07, 21:16:30 (73.169.153.194)
Excellent! That would work very well. Your measurement is quite accurate. .......
224: Tube DIY Asylum, RE: 38H OPT for 845, so so? (0.00)
Posted by Paul Joppa on 2021-04-07, 11:29:20 (73.169.153.194)
So that's 3.8 henries per Kohm, in the "acceptable" category but less than typical. This assumes that the 38 henry measurement is accurate in the bass. It's remarkably easy to measure an unrealistic v .......
225: Tube DIY Asylum, RE: 38H OPT for 845, so so? (0.00)
Posted by Paul Joppa on 2021-04-07, 09:02:48 (73.169.153.194)
To answer half of this question, we need to know the primary impedance as well as the inductance, and to answer the other half we need to know the rated power handling of the transformer and the frequ .......
226: Tube DIY Asylum, RE: Thanks - I wonder why this doesn't short? (0.00)
Posted by Paul Joppa on 2021-04-01, 21:16:04 (73.169.153.194)
Good point. I was counting on the unbypassed cathode resistor to limit the current of any arc, but it's not exactly an engineering calculation ... :^) One would think it would be a common problem, but .......
227: Tube DIY Asylum, RE: Thanks - I wonder why this doesn't short? (0.00)
Posted by Paul Joppa on 2021-04-01, 17:29:09 (73.169.153.194)
The 7199 triode looks like a 6C4, which is rated for Class C Telegraphy use with lots of grid current. That rating does not appear in the 7199 data sheet, but it does in the 6C4 sheet. .......
228: Tube DIY Asylum, RE: Bias Pots (0.00)
Posted by Paul Joppa on 2021-03-30, 09:37:01 (73.169.153.194)
OK, like this? .......
229: Tube DIY Asylum, RE: Bias Pots (0.00)
Posted by Paul Joppa on 2021-03-29, 23:28:52 (73.169.153.194)
DigiKey has this PEC pot with locking shaft. See the middle drawing on page 2 for the locking shaft version - I think that's the mil-spec version of what you want. .......
230: Tube DIY Asylum, RE: Flux Band (0.00)
Posted by Paul Joppa on 2021-03-26, 09:54:57 (73.169.153.194)
Thanks for that link! Looks really good; I'll study it carefully. .......
231: Tube DIY Asylum, RE: Flux Band (0.00)
Posted by Paul Joppa on 2021-03-26, 02:46:58 (73.169.153.194)
I am under the impression that they are not terribly effective, like maybe 6-10dB or so? - but I don't have any specific knowledge. I've seen one used with a second layer of moly-perm tape - a sort of .......
232: Tube DIY Asylum, RE: Another Transformer Topic (0.00)
Posted by Paul Joppa on 2021-03-25, 23:10:42 (73.169.153.194)
Not correct. Visualize the flux lines around the power transformer; they make loops and are going from SW to NE in the vicinity of the outputs. The outputs are oriented N-S, not perpendicular. They ar .......
233: Tube DIY Asylum, RE: That's the same fomuula I use ... (0.00)
Posted by Paul Joppa on 2021-03-23, 16:57:54 (73.169.153.194)
Higher current means you need to use larger diameter wire to maintain the same voltage drop due to wire resistance, and to prevent generating too much heat in the wire. A larger core leaves more room .......
234: Tube DIY Asylum, That's the same fomuula I use ... (0.00)
Posted by Paul Joppa on 2021-03-23, 11:38:36 (73.169.153.194)
... and every book I've seen, too. E is voltage, and B is proportional to E. The confusion arises from the distinction between magnetizing current and the current that is "transformed". .......
235: Tube DIY Asylum, RE: When you do not have the 6.3V for heaters... (0.00)
Posted by Paul Joppa on 2021-03-23, 07:46:00 (73.169.153.194)
Core flux depends on voltage, not current. Extra current just adds heat through copper resistive losses. .......
236: Tube DIY Asylum, RE: CCS question about 6SL7 Cathode Resistor (0.00)
Posted by Paul Joppa on 2021-03-19, 15:23:05 (73.169.153.194)
The 6SL7 won't do that. (it's not the current source!) At 3.75v bias (2.5mA through a 1.5K resistor) the 6SL7 needs a minimum of 350 volts on the plate to conduct the 2.5mA current. It's like trying t .......
237: SET Asylum, RE: they say the filament is still from 1963 Hawthorne smelt-nt (0.00)
Posted by Paul Joppa on 2021-03-18, 08:18:45 (73.169.153.194)
As I understand it, that may well be the most important material issue. .......
238: Tube DIY Asylum, RE: 7199 VS 6AN8 (0.00)
Posted by Paul Joppa on 2021-03-15, 15:59:36 (73.169.153.194)
We haven't found EF86s to be unstable per se, but we have found enough variation between individual samples from a variety of manufacturers to worry about. .......
239: Tube DIY Asylum, RE: Thanks, that was helpful! (0.00)
Posted by Paul Joppa on 2021-03-15, 09:06:40 (73.169.153.194)
I'd go with the 6SN7/6CG7/6FQ7 because they are more linear, and the pate-cathode voltage swing is especially large compared to the DC voltage, in a cathodyne. .......
240: Tube DIY Asylum, RE: 7199 VS 6AN8 (0.00)
Posted by Paul Joppa on 2021-03-15, 08:49:19 (73.169.153.194)
The Heathkit UA-1/UA-2/AA-61 uses the 6AN8; FWIW I believe it is well regarded. If you're going with separate envelopes, consider the EF86 - it has a reputation for especially good sound and can be v .......
241: High Efficiency Speaker Asylum, Here you go (0.00)
Posted by Paul Joppa on 2021-03-02, 08:44:38 (73.169.153.194)
http://diyaudioprojects.com/Forum/viewtopic.php?f=11&t=266 .......
242: High Efficiency Speaker Asylum, RE: Electro-Voice Sentry IV-B crossover question (0.00)
Posted by Paul Joppa on 2021-02-22, 18:15:32 (73.169.153.194)
If you choose R3 and R4 appropriately, it looks to me like no other changes are needed. Unless I'm missing something? I get R3=2.0 ohms, R4=10 ohms .......
243: Tube DIY Asylum, RE: SE UL & CFB, no NFB, and aging of tubes (0.00)
Posted by Paul Joppa on 2021-02-16, 10:46:38 (73.169.153.194)
Generally speaking, aging does not affect mu, but decreases transconductance and increases plate resistance. The term "gain" often means mu for a triode, but transconductance for a pentode. If you hav .......
244: Tube DIY Asylum, RE: I think I understand (0.00)
Posted by Paul Joppa on 2021-02-12, 14:57:13 (73.169.153.194)
Don't ignore the pot's self capacitance between terminals. It's my understanding that 10-30pF is not uncommon. .......
245: Tube DIY Asylum, RE: Question about loading for 6GK5 (0.00)
Posted by Paul Joppa on 2021-02-10, 21:40:17 (73.169.153.194)
Oh - I forgot the 5965, mu of 47 - it's fairly linear, at least on paper, and has a cathode protected from interface resistance. .......
246: Tube DIY Asylum, RE: Question about loading for 6GK5 (0.00)
Posted by Paul Joppa on 2021-02-10, 11:45:46 (73.169.153.194)
I've looked many times without finding a better high-gain triode than the 12AT7 - which is not very linear to say the least. It seems to work OK if you keep the current up (choke or current source loa .......
247: Tube DIY Asylum, RE: Question about loading for 6GK5 (0.00)
Posted by Paul Joppa on 2021-02-09, 16:21:50 (73.169.153.194)
As the 6GK5 is a variable-mu tube, keeping the load line flat is particularly important to avoid distortion. .......
248: SET Asylum, RE: Tube loading chokes? (0.00)
Posted by Paul Joppa on 2021-02-07, 22:26:19 (73.169.153.194)
By "normal range" I mean typical of the plate chokes I have measured or seen measurements of. Windings are interesting. The L/R ratio is a function of the core and gap, but any winding of the same co .......
249: SET Asylum, RE: Tube loading chokes? (0.00)
Posted by Paul Joppa on 2021-02-07, 12:38:11 (73.169.153.194)
The normalized parameter is L/R and this choke is in the normal range. The maximum DC voltage drop is 27v, about the same as the Hammond 156C (150H, 8mA, 3700 ohms) or Magnequest BCP-15 (50H, 40mA, 40 .......
250: Tube DIY Asylum, RE: I'm trying to understand the terminaology (0.00)
Posted by Paul Joppa on 2021-02-04, 21:27:12 (73.169.153.194)
The Langevin 116B and its later incarnation 5116 was SE inside the transformers, while the AM5226B was push-pull inside the transformers. .......
251: Tube DIY Asylum, A caution (0.00)
Posted by Paul Joppa on 2021-02-04, 21:07:19 (73.169.153.194)
"...Ground the center of the cap. stack and you have a 1/2 wave rectified bipolar PSU" Eli, I expect you know this, but I know not everybody does, so I'll note it here in case it helps someone else .. .......
252: Tube DIY Asylum, RE: Bad transformer? Never seen this before. (0.00)
Posted by Paul Joppa on 2021-01-27, 19:19:17 (73.169.153.194)
Is the first filter capacitor in backwards? .......
253: High Efficiency Speaker Asylum, RE: It depends... (0.00)
Posted by Paul Joppa on 2021-01-26, 05:52:50 (73.169.153.194)
I think you said your sub was a folded horn, so I have to ask what the path length is? Just to clarify the time delay difference. .......
254: Tube DIY Asylum, RE: Strange tube amp, questions (0.00)
Posted by Paul Joppa on 2021-01-24, 23:05:19 (73.169.153.194)
The heaters are in series - 2x50 + 12 = 112 volts. It runs off the power line directly, no transformer, not really safe. It would never get a UL approval today (or anytime in the last 50 years ...) :: .......
255: High Efficiency Speaker Asylum, Thanks... (0.00)
Posted by Paul Joppa on 2021-01-24, 22:57:32 (73.169.153.194)
Too many acronyms for me! .......
256: High Efficiency Speaker Asylum, OK, I give up - what is an "LP"? (0.00)
Posted by Paul Joppa on 2021-01-24, 20:10:15 (73.169.153.194)
12" vinyl 33rpm recording? LowPass filter? Laser Player? Lower perimeter? .......
257: SET Asylum, RE: Chinese 300B (0.00)
Posted by Paul Joppa on 2021-01-22, 20:27:26 (73.169.153.194)
Many tubes will drift during the first 100 hours or so, as the cathode finishes forming I presume. It's worth checking again when they are run in. .......
258: Tube DIY Asylum, RE: The 3rd harmonic (0.00)
Posted by Paul Joppa on 2021-01-04, 11:38:15 (73.169.153.194)
Thanks, Ralph - that's a very clear expansion, and a new perspective for me. Much appreciated! I've only heard a couple push-pull DHT amps with no feedback, and I think both of them had substantial 2n .......
259: Tube DIY Asylum, It was probably the 125E (0.00)
Posted by Paul Joppa on 2021-01-04, 08:26:12 (73.169.153.194)
I played with them some 20 years ago. They were at the time advertised as "single ended or push-pull" but currently they are said to be push-pull only - which I can confirm based on measurements I mad .......
260: Tube DIY Asylum, RE: I got a question (0.00)
Posted by Paul Joppa on 2020-12-31, 15:56:05 (73.169.153.194)
"I agree with a bit of it, but one part I do not is the special case of the 3rd harmonic. The ear treats this much the same way as the 2nd; to this end the comment about the 3rd being more audible tha .......
261: Tube DIY Asylum, RE: SE 6V6 E-Linear : found my schematic ... (0.00)
Posted by Paul Joppa on 2020-12-30, 13:43:19 (73.169.153.194)
Thanks for clarifying. FWIW, I've been calling it a transimpedance stage - current in, voltage out. I don't expect it to catch on though ... :^) .......
262: Tube DIY Asylum, RE: SE 6V6 E-Linear : found my schematic ... (0.00)
Posted by Paul Joppa on 2020-12-30, 09:54:44 (73.169.153.194)
By that definition, it seems little different from an anode follower, or Schade feedback stage from 1938 - unless I'm missing something? .......
263: Tube DIY Asylum, RE: Help needed, very confused. (0.00)
Posted by Paul Joppa on 2020-12-29, 22:09:35 (73.169.153.194)
The 27 heater is not tolerant of much heater/cathode voltage difference; recommended practice is to tie the cathode to the filament voltage center-tap. .......
264: Tube DIY Asylum, RE: SE 6V6 E-Linear : found my schematic ... (0.00)
Posted by Paul Joppa on 2020-12-29, 22:00:38 (73.169.153.194)
Yeah, it's not e-linear without the screen going to the UL tap. The driver rp and its plate and cathode resistances are critical to getting the feedback right while maintaining drive capability, so e .......
265: Tube DIY Asylum, RE: yep (0.00)
Posted by Paul Joppa on 2020-12-27, 13:44:41 (73.169.153.194)
That's true, but I was mostly thinking of matching the parafeed capacitance to the plate choke inductance, so they partially cancel each other's reactance. .......
266: Tube DIY Asylum, RE: you could biamp (0.00)
Posted by Paul Joppa on 2020-12-27, 10:16:50 (73.169.153.194)
One of the benefits of parafeed is the ability to keep the load more resistive around the LF cutoff. Just sayin' ... .......
267: Tube DIY Asylum, RE: Hammond 125ESE bandwidth when used at lower power? (0.00)
Posted by Paul Joppa on 2020-12-25, 22:03:04 (73.169.153.194)
I don't know how they are wound, so it's hard to answer. The secondary must be contiguous, of course, but it may be made of several different diameter wires, and could be non-sequentially wound. These .......
268: Tube DIY Asylum, RE: Hammond 125ESE bandwidth when used at lower power? (0.00)
Posted by Paul Joppa on 2020-12-25, 17:27:26 (73.169.153.194)
I have not measured any of the 125xSE units, but I did do an analysis of the published specs with some plausible assumptions a few months ago. I concluded that the 125ESE should work quite well with a .......
269: Tube DIY Asylum, Thank You !! (0.00)
Posted by Paul Joppa on 2020-12-25, 07:15:43 (73.169.153.194)
And I'll join you in wishing everyone here has a very merry Christmas (or however you celebrate the solstice) and a better New Year. .......
270: High Efficiency Speaker Asylum, RE: mids (0.00)
Posted by Paul Joppa on 2020-12-14, 18:31:43 (73.169.153.194)
How about the 5-inch Audax ? The specs look good - has anyone here heard it? .......
271: Tube DIY Asylum, RE: Reduction of Available Plate Voltage (0.00)
Posted by Paul Joppa on 2020-12-14, 12:40:23 (73.169.153.194)
In some situations, that will be the case; it really depends on the specific situation. Here's an example: Suppose you are making a 2A3 amp using a 6SN7 driver. At the standard operating point, the 2A .......
272: Tube DIY Asylum, RE: Basic Drive Voltage Question (0.00)
Posted by Paul Joppa on 2020-12-13, 19:30:30 (73.169.153.194)
Resistor or current source loading reduces the available plate voltage, limiting headroom and thus increasing distortion. .......
273: SET Asylum, RE: Mastersound Reference 845 Amp (0.00)
Posted by Paul Joppa on 2020-12-10, 23:50:13 (73.169.153.194)
I don't think it's a non-issue, though there's no evidence whether or not it's the main issue. With 10dB increase of power, the 2nd harmonic distortion is increased by a factor of 3, 3rd harmonic by .......
274: Tube DIY Asylum, RE: Basic Drive Voltage Question (0.00)
Posted by Paul Joppa on 2020-12-10, 09:00:33 (73.169.153.194)
Yes, your calculation is correct. With a choke load, the midband gain is essentially equal to mu. In the bass, you have to use impedance rather than resistance, allowing for the 90 degree phase differ .......
275: Tube DIY Asylum, RE: Basic Drive Voltage Question (0.00)
Posted by Paul Joppa on 2020-12-09, 18:09:58 (73.169.153.194)
Only if the driver plate load RL and output grid resistor Rg are much much greater than the plate resistance rp. In the real world :^) the load on the plate is the parallel combination of RL and Rg in .......
276: Tube DIY Asylum, RE: RCA Application Note (0.00)
Posted by Paul Joppa on 2020-12-03, 11:18:12 (73.169.153.194)
That's new to me, too - much appreciated! I see this Application Note is dated 1937. The early heater-cathode tubes like 27, 56/76, etc. are known to have inferior heater-cathode maximum insulation vo .......
277: Tube DIY Asylum, RE: B+ voltage appears to crash when tubes wired in (0.00)
Posted by Paul Joppa on 2020-11-25, 15:11:44 (73.169.153.194)
Without a circuit, it's harder to tell. But a classic is installing the 45 in the wrong socket holes ... .......
278: High Efficiency Speaker Asylum, RE: Curious about what speaker characteristics (0.00)
Posted by Paul Joppa on 2020-11-23, 20:24:33 (73.169.153.194)
In this case, I'm just talking about bass. The low damping factor raises the effective Q of the driver, while a bigger magnet decreases it. So you can make the same alignment in the same box with the .......
279: High Efficiency Speaker Asylum, RE: Speaker driver or speaker box? (0.00)
Posted by Paul Joppa on 2020-11-23, 13:13:39 (73.169.153.194)
Apologies - I have corrected my post. .......
280: High Efficiency Speaker Asylum, RE: Bob Carver tweaked a SS amp to sound exacly like a CJ years ago... (0.00)
Posted by Paul Joppa on 2020-11-20, 20:09:38 (73.169.153.194)
Some speakers (not many!) are designed for use with low-damping-factor amps. Interestingly, it has the advantage of "cheating" on Hoffman's Iron Law; you can get a bit more efficiency from a bigger ma .......
281: Tube DIY Asylum, RE: Decrease grid leak resistor value? (0.00)
Posted by Paul Joppa on 2020-11-20, 12:27:25 (73.169.153.194)
It does resemble grid emission, which usually happens when some of the cathode's emissive material gets deposited on the grid. That might happen if the tube gets too hot, or possibly if the tube is sl .......
282: High Efficiency Speaker Asylum, RE: If it is high level HD..... (0.00)
Posted by Paul Joppa on 2020-11-20, 12:09:59 (73.169.153.194)
The first amplifier I built came from the pages of Popular Electronics, in 1962 I think - I was a teen at the time. It used the then-new "transistors." Powered by four D-cells, the speaker was the col .......
283: Tube DIY Asylum, Leaking PIO coupling caps? nt (0.00)
Posted by Paul Joppa on 2020-11-18, 11:38:04 (73.169.153.194)
nt .......
284: Tube DIY Asylum, RE: Power supply and filament heater question (0.00)
Posted by Paul Joppa on 2020-11-18, 11:28:59 (73.169.153.194)
That 410 volts with a 3300 ohm cathode resistor suggest strongly that you are looking at a direct-coupled amp. .......
285: Tube DIY Asylum, RE: Transformer for Japanese component (0.00)
Posted by Paul Joppa on 2020-11-16, 21:18:26 (73.169.153.194)
120v at 60Hz produces the same magnetic flux as 100V at 50Hz, so stepping down the voltage without changing the frequency should actually reduce the strain on the power transformer. .......
286: Tube DIY Asylum, RE: Orientation indeed. Including three dimensions (0.00)
Posted by Paul Joppa on 2020-11-07, 22:17:41 (73.169.153.194)
'Can you tell the circuit began life on the famous "cocktail napkin in a crummy chinese restaurant at CES" by Doc and John Tucker?' Once I saw the insides, yeah it looks like the kind of stuff we were .......
287: Tube DIY Asylum, RE: Preamp: 5842 w/output transformers (0.00)
Posted by Paul Joppa on 2020-11-07, 15:15:10 (73.169.153.194)
Thanks for the reference! I'm glad that rule of thumb has worked out for you. I must admit however that I have no recollection of that post, or what the context was. In any case, my thinking has evolv .......
288: Tube DIY Asylum, RE: I put Lithium Grease on a Bipolar Transistor (0.00)
Posted by Paul Joppa on 2020-10-27, 07:53:32 (73.169.153.194)
Google "lithium bipolar" for a clue ... .......
289: Tube DIY Asylum, RE: How rugged are vintage 2A3 tubes? (0.00)
Posted by Paul Joppa on 2020-10-23, 16:10:15 (73.169.153.194)
Here's a couple data points: * 2A3 reference operating point is 250v @ 60mA - equal to the maximum spec. * 300B reference is 350v @ 60mA - 21 watts; max spec is 36 watts (1950 data sheet values) Eithe .......
290: Tube DIY Asylum, Thanks for the kind words! (0.00)
Posted by Paul Joppa on 2020-10-20, 22:38:21 (73.169.153.194)
Both of the triodes in a 6DN7/6FJ7 bottle are more linear than the usual dissimilar dual triode TV tubes - I sometimes say it's the poor man's 45 :^) Since we put in the better iron around a decade ag .......
291: Tube DIY Asylum, RE: How much current can a 26 tube take? (0.00)
Posted by Paul Joppa on 2020-10-20, 21:05:30 (73.169.153.194)
At that time (introduced in 1927), maximum ratings were not generally specified, other than plate voltage. I would not want to exceed that rating on such an old, classic tube! It's basically an 01A wi .......
292: High Efficiency Speaker Asylum, RE: Lansing Heritage Forum (0.00)
Posted by Paul Joppa on 2020-09-27, 20:26:24 (73.169.153.194)
Perhaps you didn't check the box that says you agree to abide by the rules? This like that often happen to me, and it's usually something trivial that I missed the first time. .......
293: Tube DIY Asylum, RE: operation point 330b xls (0.00)
Posted by Paul Joppa on 2020-09-26, 08:11:26 (73.169.153.194)
It's simpler if you do a graphical construction - I just set the maximum current (at zero grid bias) to twice the quiescent current, and used the 3/2 power rule to derive an equation. .......
294: Tube DIY Asylum, RE: operation point 330b xls (0.00)
Posted by Paul Joppa on 2020-09-25, 21:55:36 (73.169.153.194)
The factor 2.38 is three divided by the cube root of 2, in case anyone wondered. :^) It's an arbitrary reference point, chosen partly for mathematical convenience, but it gives a pretty good point fo .......
295: Tube DIY Asylum, RE: operation point 300b xls (0.00)
Posted by Paul Joppa on 2020-09-23, 00:06:18 (73.169.153.194)
I entirely agree with Tre''s post below. I'd like to add what I think is a plausible reason for wanting one of these "high distortion" operating points. The tube plate curves bunch up at low currents/ .......
296: SET Asylum, RE: Dynamic and Detailed 300B SET amp (0.00)
Posted by Paul Joppa on 2020-09-20, 12:08:20 (73.169.153.194)
Perception is a gestalt thing, science is usually analytical, so it's always difficult to be sure of how they are related So I don't have any clear answers, but I do have one piece of theory that is a .......
297: Tube DIY Asylum, RE: CCS Current Set Question (0.00)
Posted by Paul Joppa on 2020-09-16, 08:12:24 (73.169.153.194)
Thanks for the link - I didn't know he had a site. Yeah, I've done pentodes with CS loads too, it's just a little more complicated. .......
298: Tube DIY Asylum, RE: CCS Current Set Question (0.00)
Posted by Paul Joppa on 2020-09-15, 11:53:43 (73.169.153.194)
You don't get a choice. If you run the current high, the plate voltage will rise until the tube consumes the current. That's why you usually don't see CS loads on pentodes. .......
299: High Efficiency Speaker Asylum, RE: Which are the most efficient speakers? (0.00)
Posted by Paul Joppa on 2020-09-03, 10:45:23 (73.169.153.194)
The problem with using heat is that the efficiency is low, so the accuracy of heat measurement must be very high. If efficiency is 5%, that would be 100watts in minus 95 watts dissipated, so even +/- .......
300: High Efficiency Speaker Asylum, RE: Which are the most efficient speakers? (0.00)
Posted by Paul Joppa on 2020-09-03, 08:06:48 (73.169.153.194)
Technically, efficiency is sound power output divided by electrical power input. Sound power (in watts) is measured either by integrating over a surface enclosing the source in an anechoic chamber or .......
301: Tube DIY Asylum, RE: OK folks, 16 mv across 10 ohms (dummy load on the bench) is only 1.6 ma... (0.00)
Posted by Paul Joppa on 2020-08-31, 13:27:15 (73.169.153.194)
I get 25 microwatts, which is 45dB below 1 watt, so 106 - 45 = 61dB - about the level of normal conversation. .......
302: Tube DIY Asylum, RE: New project, voltage checks good, blows fuse after 45 minutes and power transformer hellaciously hot and odd smell (0.00)
Posted by Paul Joppa on 2020-08-30, 23:10:32 (73.169.153.194)
I'm not sure if I was clear; I certainly didn't say what I meant very well. Let me make another attempt: If you had a fullwave bridge on a transformer rated 58mA RMS, you might reasonably expect to ge .......
303: Tube DIY Asylum, RE: New project, voltage checks good, blows fuse after 45 minutes and power transformer hellaciously hot and odd smell (0.00)
Posted by Paul Joppa on 2020-08-30, 17:08:54 (73.169.153.194)
The 58mARMS is for the whole winding. For FWCT you would get 1.414 times as much current, i.e. 82mA. It's complicated, and the current version of PSUD has some issues with how it reports current numbe .......
304: Tube DIY Asylum, RE: New project, voltage checks good, blows fuse after 45 minutes and power transformer hellaciously hot and odd smell (0.00)
Posted by Paul Joppa on 2020-08-29, 16:07:40 (73.169.153.194)
It was more or less standard in the past to spec the DC current assuming a cap-input filter and an appropriates rectifier tube. That is more of a problem now that many are using solid-state rectifiers .......
305: Tube DIY Asylum, RE: How big a choke.... (0.00)
Posted by Paul Joppa on 2020-08-29, 08:27:22 (73.169.153.194)
Thanks Dave for posting those details. They agree with my memory - it's been some 15 years since I did this. I think of it as an LR filter, analogous to an RC filter. .......
306: Tube DIY Asylum, RE: How big a choke.... (0.00)
Posted by Paul Joppa on 2020-08-29, 08:09:14 (73.169.153.194)
You are right - thanks for catching that! I guess my eyes are getting old ... I'll edit my post. .......
307: Tube DIY Asylum, RE: Could use some help Trouble Shooting my Welborne laurel 300B Monoblock ............... (0.00)
Posted by Paul Joppa on 2020-08-28, 13:18:08 (73.169.153.194)
Pull out the rectifier and try again, checking to see if all the heaters / cathodes glow. If so, then check the high voltage winding AC voltages to be sure the power transformer is OK. If it is, then .......
308: Tube DIY Asylum, RE: Steve Bench dht ac filament hum reduction circuit (0.00)
Posted by Paul Joppa on 2020-08-28, 00:21:36 (73.169.153.194)
It worked for Bench, not so well for me, but I have some doubts that I understood it and implemented it correctly at the time. That was 20 years ago; I would not defend my remarks at this point. ::: T .......
309: Tube DIY Asylum, RE: How big a choke.... (0.00)
Posted by Paul Joppa on 2020-08-28, 00:16:09 (73.169.153.194)
I have, with some success, used a Hammond [Edit: 155B, not 156B] 6mH at 2.0 amps and 0.3 ohms. On a rated 2-amp 6.3v winding, and using 5-amp Schottky rectifiers, it made about 4.8vDC. Higher-rated re .......
310: Tube DIY Asylum, RE: Steve Bench dht ac filament hum reduction circuit (0.00)
Posted by Paul Joppa on 2020-08-27, 21:52:15 (73.169.153.194)
Probably you could adapt it to a direct-coupled circuit. The original was done with fixed bias; Dan Schmalle and I tried it with cathode bias. It wasn't very successful - hard to adjust and didn't can .......
311: Tube DIY Asylum, RE: Steve Bench dht ac filament hum reduction circuit (0.00)
Posted by Paul Joppa on 2020-08-25, 09:57:54 (73.169.153.194)
Actually, the original first widely available vacuum tube, the UV-201 (01A was a refined version) used 5v DC, derived from 6-v car batteries. This 5v standard was adopted by Western Electric and maint .......
312: Tube DIY Asylum, RE: Amp Issue (0.00)
Posted by Paul Joppa on 2020-08-14, 18:54:20 (73.169.153.194)
I can however easily imagine a marginal solder connection to the ground leg of a pot failing in a temperature-sensitive way. Just sayin' ... .......
313: Tube DIY Asylum, RE: Input transformer (0.00)
Posted by Paul Joppa on 2020-08-14, 18:47:06 (73.169.153.194)
That clarifies the situation. For the 1:2 connection, all four primaries are in series so the input impedance is 16 times greater than the 1:8 connection where the primaries are all in parallel. In th .......
314: Tube DIY Asylum, RE: Input transformer (0.00)
Posted by Paul Joppa on 2020-08-14, 09:31:37 (73.169.153.194)
The Zobel damps the transformer's high frequency resonance - in this case, above about 7kHz. Increasing the resistance will reduce the damping. How much of a problem this might be depends on the trans .......
315: Tube DIY Asylum, RE: Input transformer (0.00)
Posted by Paul Joppa on 2020-08-13, 20:25:56 (73.169.153.194)
If it's a 1:8 turns ration and the load is 4700 ohms, then the input impedance of the transformer is 73 ohms. Applying the usual recommendation of a 10:1 load:driver ratio, the output impedance needed .......
316: SET Asylum, Not really (0.00)
Posted by Paul Joppa on 2020-08-09, 08:02:17 (73.169.153.194)
Think of the load line oval at low frequency - the peak current demand depends primarily on the inductive reactance and is relatively insensitive to the resistive part. .......
317: High Efficiency Speaker Asylum, RE: Have you heard the Sweet Sixteen speakers? link (0.00)
Posted by Paul Joppa on 2020-08-09, 07:53:18 (73.169.153.194)
It sounded like a table radio - no bass, crappy/weak treble, ragged midrange - except it could play louder before distortion became prominent, and it was very efficient. Nevertheless, it always fasci .......
318: High Efficiency Speaker Asylum, RE: Have you heard the Sweet Sixteen speakers? link (0.00)
Posted by Paul Joppa on 2020-08-06, 16:18:46 (73.169.153.194)
Yes, I remember when that article came out, and a few years later in college they had one in my preferred coffeehouse. Sounded better than a cheap AC/DC table radio, but not much - at that time I had .......
319: High Efficiency Speaker Asylum, RE: A Simple Question I don't Know The Answer To! (0.00)
Posted by Paul Joppa on 2020-07-07, 23:27:34 (73.169.153.194)
You are right about the power; I'll just add that there's a small decrease in measurable distortion (probably not audible) and a greater damping factor (probably audible). There are a lot of ways to d .......
320: Tube DIY Asylum, RE: Why nickel? (0.00)
Posted by Paul Joppa on 2020-07-05, 08:46:52 (73.169.153.194)
Cobalt is very expensive - IIRC Magnequest lucked into a small quantity of laminations at a bargain price, which fueled at least some of the short-lived offerings. Technically,cobalt laminations have .......
321: Tube DIY Asylum, RE: Why nickel? (0.00)
Posted by Paul Joppa on 2020-07-03, 15:35:50 (73.169.153.194)
Technically, cores alloys containing nickle have greater permeability and less hysteresis loss, but a lower saturation flux. In practice, those things mean lower distortion, greater resolution, and yo .......
322: Tube DIY Asylum, RE: Question about OPTs for SET (0.00)
Posted by Paul Joppa on 2020-07-01, 15:42:45 (73.169.153.194)
Dave - Yes, my post was over-simplified. Here's a more detailed discussion: A 2.5K transformer is typically designed for a 2A3 with 800 ohms plate resistance. A 5K transformer might typically be desig .......
323: Tube DIY Asylum, RE: Question about OPTs for SET (0.00)
Posted by Paul Joppa on 2020-06-29, 08:24:50 (73.169.153.194)
Operating at a reflected load of 5K compared to 2.5K will lose an octave of bass, so you want an excess of inductance. Based on my experience with amps for speakers, a minimum of about 5 henries per K .......
324: Tube DIY Asylum, RE: cnc chassis ? (0.00)
Posted by Paul Joppa on 2020-06-28, 08:21:11 (73.169.153.194)
What do you have to provide - DXF files or similar? .......
325: Tube DIY Asylum, RE: cnc chassis ? (0.00)
Posted by Paul Joppa on 2020-06-27, 21:30:14 (73.169.153.194)
Front Panel Express is convenient and easy to use. They can make complete boxes, or you can just make the top plate and mount it on an upside down Hammond box. .......
326: SET Asylum, RE: Thanks... (0.00)
Posted by Paul Joppa on 2020-06-16, 08:35:13 (73.169.153.194)
Yes, the weak links in the original Paramour from 20 years ago were the plate chokes - and the output transformers. (That's a big part of what made it inexpensive, of course ...) It's a long story, b .......
327: SET Asylum, RE: Only heard the 5670 version... (0.00)
Posted by Paul Joppa on 2020-06-15, 21:22:40 (73.169.153.194)
That's the 396A. .......
328: SET Asylum, RE: "a more linear driver tube"... (0.00)
Posted by Paul Joppa on 2020-06-15, 08:55:37 (73.169.153.194)
Yes, answering questions is OK - and I am happy to do it. You used the term "original Paramount" - that used a 12AT7. There were some issues in certain specific cases which led to a revision incorpora .......
329: Tube DIY Asylum, RE: Question about 6922 design (0.00)
Posted by Paul Joppa on 2020-06-13, 21:34:21 (73.169.153.194)
I agree. For what it's worth, I recall people saying (some 20years ago?) that 6DJ8s fail much more rapidly if their quiescent plate voltage exceeds 90vDC; however 6922s do not suffer from this. I've .......
330: SET Asylum, RE: If I were going to ask the question... (0.00)
Posted by Paul Joppa on 2020-06-13, 20:37:48 (73.169.153.194)
MonAmour has DC filaments, better iron, and a more linear driver tube, compared to the original Paramount. It is not direct coupled, which the 2A3 version of Paramount was. I am limited in what I shou .......
331: SET Asylum, RE: why not outsource overseas to increase margin ? (0.00)
Posted by Paul Joppa on 2020-06-10, 09:54:30 (73.169.153.194)
Reliability and responsiveness are the main reasons. The ability to work closely together is especially important when doing a non-standard custom design. And as many small manufacturers have found, o .......
332: SET Asylum, RE: Good driver tube for PX25 / DET5 (0.00)
Posted by Paul Joppa on 2020-06-09, 14:30:52 (73.169.153.194)
I found some curves for the 3A/110B which look very good; haven't found any for the Ca. Ca has a mu of ~8. .......
333: SET Asylum, RE: Good driver tube for PX25 / DET5 (0.00)
Posted by Paul Joppa on 2020-06-09, 07:56:33 (73.169.153.194)
It's a tradeoff. With a plate choke and capacitor you get a high impedance and excellent power supply rejection ratio but you need a really good coupling capacitor; with a transformer you still get th .......
334: SET Asylum, RE: Good driver tube for PX25 / DET5 (0.00)
Posted by Paul Joppa on 2020-06-08, 23:52:35 (73.169.153.194)
If you want the character of the DET5 to shine, then you want as linear a driver as possible. It's most important to find a tube with a large enough region of uniform mu, and operate it there. I use t .......
335: SET Asylum, RE: Do tell... (0.00)
Posted by Paul Joppa on 2020-06-06, 22:17:29 (73.169.153.194)
No, we consider that proprietary. But you would not likely have heard of them - nothing fancy, just a small-town American factory that happens to do really good, reliable custom work for us. ::: TOPIC .......
336: SET Asylum, RE: Could be very good... (0.00)
Posted by Paul Joppa on 2020-06-04, 08:01:32 (73.169.153.194)
The iron in current Stereomour and other Bottlehead amps is custom made for us; they are my designs. .......
337: SET Asylum, RE: 300/76/6sn7 Hogan amp - Repaired? Cap questions (0.00)
Posted by Paul Joppa on 2020-06-02, 13:39:47 (73.169.153.194)
Good call. Yes, the output signal current flows through the power supply, mostly through the last filter capacitor, so that would have some effect. At 20Hz the reactance of 47uF is 160 ohms - not insi .......
338: SET Asylum, RE: 300/76/6sn7 Hogan amp - Repaired? Cap questions (0.00)
Posted by Paul Joppa on 2020-06-01, 16:43:16 (73.169.153.194)
Assuming the caps are the power supply filters, it won't change B+ by much. It will however increase ripple (hum), which may or may not be audible. .......
339: Tube DIY Asylum, RE: Suggestion for a triode, about 20mA, gain about 20? (0.00)
Posted by Paul Joppa on 2020-05-26, 20:41:09 (73.169.153.194)
Well, the sound of the music when using the tube ... :^) .......
340: Tube DIY Asylum, RE: Suggestion for a triode, about 20mA, gain about 20? (0.00)
Posted by Paul Joppa on 2020-05-26, 17:10:27 (73.169.153.194)
7044 mu is 21; otherwise similar to 5687. 12A4 mu is 20. It's unusually linear, as is a 6SN7. Some people don't like the sound, but I don't know why; never heard it myself. .......
341: High Efficiency Speaker Asylum, RE: High efficiency loudspeaker options (0.00)
Posted by Paul Joppa on 2020-05-15, 17:56:42 (73.169.153.194)
I don't have a list, but I'll offer an overview of the landscape, which I hope will help focus your research. As I see it, there are two main branches - vintage mainstream speakers and modern boutique .......
342: Tube DIY Asylum, RE: Question on the 958A "Sound Processor" (0.00)
Posted by Paul Joppa on 2020-05-13, 20:59:55 (73.169.153.194)
The 68 ohm resistor sets the bias (6.8 volts, since there is 100mA flowing through it). .......
343: Tube DIY Asylum, RE: RCA 816 MV (0.00)
Posted by Paul Joppa on 2020-05-11, 15:08:58 (73.169.153.194)
IIRC, it's a matter of getting and keeping the temperature inside the envelope in the right range for the pool of mercury. Read the data sheet. .......
344: SET Asylum, RE: You have posts where people say "This is a great idea!"? (0.00)
Posted by Paul Joppa on 2020-04-29, 09:18:45 (73.169.153.194)
I checked, and see that the version 2 manual says 6SL7s on p.3 (specs) but still shows 6SN7s on the tube location diagram, p.8. I was hoping to see a circuit diagram; I think these are SRPP stages? I .......
345: Tube DIY Asylum, RE: battery in series with the grid (0.00)
Posted by Paul Joppa on 2020-04-17, 11:19:07 (73.169.153.194)
There was never (to my knowledge) any consensus reason, just the observation of damaged batteries. The grid must have a DC reference, whether or not there is a coupling cap upstream of it - usually th .......
346: Tube DIY Asylum, RE: battery in series with the grid (0.00)
Posted by Paul Joppa on 2020-04-17, 09:08:42 (73.169.153.194)
There have been reports of damaged batteries in the past - but I haven't heard anything in the last decade. .......
347: Tube DIY Asylum, RE: Need help selecting a 5.0volt D.C. module for 300B filament , (0.00)
Posted by Paul Joppa on 2020-04-10, 11:42:03 (73.169.153.194)
In some cases, a simple FW bridge of Schottky diodes and a choke-input filter, powered from a 6.3v winding, will do the job. Hammond makes some very small chokes, for example 154B. Getting enough volt .......
348: Tube DIY Asylum, RE: Help with Toroidal transformer (0.00)
Posted by Paul Joppa on 2020-02-27, 19:55:05 (73.169.153.194)
You can run them at the rated current per winding - that's a heat limit - but the winding resistance is doubled, so the regulation is twice the original. For a transformer this big, that's probably no .......
349: Tube DIY Asylum, RE: Help with Toroidal transformer (0.00)
Posted by Paul Joppa on 2020-02-27, 14:00:43 (73.169.153.194)
For the lowest induced hum, put the primary windings in series (run a 240v transformer on 120v). This cuts the flux density in half, greatly reducing the radiated field and any mechanical vibration. P .......
350: SET Asylum, RE: The longest lasting Triode in the world (0.00)
Posted by Paul Joppa on 2020-02-27, 13:53:21 (73.169.153.194)
My candidate is the 175HQ repeater amplifiers which Bell Labs made for underwater telephone cables. The first cable had 102 amplifiers, three tubes each, and operated continuously for 22 years with ze .......
351: Tube DIY Asylum, RE: Are you convinced what this guy said about 845 (0.00)
Posted by Paul Joppa on 2020-02-25, 15:55:41 (73.169.153.194)
It's just a matter of inductance and transformer $ize ... :^) The Magnequest FS-030 is about 40 henries and will get down there pretty deep and still clean. It's just big and heavy, probably 2-3 times .......
352: High Efficiency Speaker Asylum, Not news, indeed! (0.00)
Posted by Paul Joppa on 2020-02-18, 20:46:42 (73.169.153.194)
I first learned about throat distortion about 1969 - from Leo Beranek's 1954 book "Acoustics". Later I learned that the analysis goes back to the thirties, maybe the twenties. .......
353: High Efficiency Speaker Asylum, RE: spend some time with a 1970s pair of Heresys (0.00)
Posted by Paul Joppa on 2020-02-18, 06:50:09 (73.169.153.194)
You're at least safe in concluding you don't have a problem :^) I am using horn smyself with really small mouths; they honk but I got used to it quickly and it does not bother me. Hearing is so indivi .......
354: High Efficiency Speaker Asylum, RE: spend some time with a 1970s pair of Heresys (0.00)
Posted by Paul Joppa on 2020-02-17, 21:15:32 (73.169.153.194)
The terms "squawk" and "honk" appear frequently as issues with horns. I've never seen a useful description of what exactly they mean. Perhaps they merely mean the kind of unpleasant sound that bad hor .......
355: High Efficiency Speaker Asylum, RE: what is the least "shouty" horn speaker? (0.00)
Posted by Paul Joppa on 2020-02-15, 20:43:41 (73.169.153.194)
There's a long and detailed thread on the Lansing Heritage site on pretty much just this question - the link is below. It's probably more than anyone wants to know :^) but I think it's technically ver .......
356: Tube DIY Asylum, RE: Math help, Dynaco Pas 3x (0.00)
Posted by Paul Joppa on 2020-02-08, 08:11:21 (73.169.153.194)
I don't know enough to answer that question. The output impedance of the phono stage should be low at high frequencies since the feedback is greater, but I think much depends on things like the capaci .......
357: Tube DIY Asylum, RE: IT as plate choke (0.00)
Posted by Paul Joppa on 2020-02-07, 15:43:41 (73.169.153.194)
It's a single winding of bifilar wire when they are paralleled. .......
358: Tube DIY Asylum, RE: Math help, Dynaco Pas 3x (0.00)
Posted by Paul Joppa on 2020-02-07, 15:37:17 (73.169.153.194)
Because of the feedback equalization, the output impedance will be a strong function of frequency. .......
359: Tube DIY Asylum, RE: Tranny coupling versus cap coupling (0.00)
Posted by Paul Joppa on 2020-02-05, 22:21:06 (73.169.153.194)
Haha! Yeah, now that you mention it, the original Paramour is 20 years old this year. Time flies when you're having fun! Actually a number of people have used our headphone amps as preamps, including .......
360: Tube DIY Asylum, RE: Tranny coupling versus cap coupling (0.00)
Posted by Paul Joppa on 2020-02-03, 21:57:35 (73.169.153.194)
An often-overlooked use of a preamp output transformer is to reduce the noise floor of the preamp. It also eats up overload margin, but most tube preamps have an over-abundance of that. For the same r .......
361: Tube DIY Asylum, RE: SMPS DC heaters for SE 6AQ5 amp ... (0.00)
Posted by Paul Joppa on 2019-12-20, 20:36:31 (73.97.163.58)
Just a caution - if one of the tubes' heaters quits or a tube is pulled, the voltage will rise. Better to use separate resistors for each tube. .......
362: Tube DIY Asylum, RE: MF grid for grid stoppers- a retrovert perspective (0.00)
Posted by Paul Joppa on 2019-12-20, 13:58:08 (73.97.163.58)
The only problem with grid stoppers that I can recall is fragile carbon composition resistors, which can (and do) break mechanically under stress from installation or tube swapping. We've been using c .......
363: Tube DIY Asylum, RE: MF grid for grid stoppers- a retrovert perspective (0.00)
Posted by Paul Joppa on 2019-12-20, 11:35:30 (73.97.163.58)
I recall some posts (and personal conversation) with VoltSecond, who has not been very active on these forums the last few years, but has extensive professional experience with industrial high-voltage .......
364: Tube DIY Asylum, +1 (nt) (0.00)
Posted by Paul Joppa on 2019-12-06, 08:25:22 (73.97.163.58)
nt .......
365: High Efficiency Speaker Asylum, RE: Efficient speaker suggestions please (0.00)
Posted by Paul Joppa on 2019-12-01, 08:57:09 (73.97.163.58)
FYI, here's my more "recent" FAQ post, with a reference to the original: https://db.audioasylum.com/mhtml/m.html?forum=hug&n=156394&highlight=FAQ&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dhug%26sear .......
366: Tube DIY Asylum, RE: Need advice, low plate voltage on 5687 (0.00)
Posted by Paul Joppa on 2019-11-27, 12:12:35 (73.97.163.58)
Draw the load line on the plate curves. If that's not clear, google "load line" "plate curves" .......
367: Tube DIY Asylum, RE: Need advice, low plate voltage on 5687 (0.00)
Posted by Paul Joppa on 2019-11-26, 22:55:38 (73.97.163.58)
From the plate curves (I used the Raytheon 5687-WA data sheet), I get 45v at the zero-bias line, so your peak negative output is 140-45=95 volts. In the positive direction at 95+140=230v the driver is .......
368: Tube DIY Asylum, RE: Simple screen regulation for Scott LK-48(222C) (0.00)
Posted by Paul Joppa on 2019-11-25, 16:28:39 (73.97.163.58)
I've done the "simple SS voltage follower that is fed by a less power hungry divider," and it worked well. The problem with a Zener string or other shunt reg is that the quiescent current of the shunt .......
369: Tube DIY Asylum, RE: Paul (0.00)
Posted by Paul Joppa on 2019-11-25, 16:18:40 (73.97.163.58)
Yeah, it's a challenge when working outside the "recommended operation" data. But basically if current drops a little faster than voltage (the 3/2 power law) then the operating point looks similar in .......
370: Tube DIY Asylum, RE: Need advice, low plate voltage on 5687 (0.00)
Posted by Paul Joppa on 2019-11-25, 09:59:54 (73.97.163.58)
By my rule, at 140v you would want something around 14mA; 9mA is a bit thin, but not out of reason. If that stage is resistor-loaded with 5K ohms (70v/14mA) then the plate could swing 70v peak, which .......
371: Tube DIY Asylum, RE: Need advice, low plate voltage on 5687 (0.00)
Posted by Paul Joppa on 2019-11-25, 08:35:40 (73.97.163.58)
You will be fine. At 76v plate to cathode, the 5687 runs 6mA with 3v bias, which is very reasonable. We have run 12AU7s, which have the same gain, at 70v/3.5mA with great success. The 5687 has a lowe .......
372: SET Asylum, RE: Wait a minute here ... (0.00)
Posted by Paul Joppa on 2019-11-24, 21:43:13 (73.97.163.58)
Can't say I know a lot about hexfreds, but no problem with email - my Bottlehead address should work. .......
373: SET Asylum, Wait a minute here ... (0.00)
Posted by Paul Joppa on 2019-11-20, 23:14:38 (73.97.163.58)
So I looked at the schematic, and it looks like all you need is to augment the 50-watt resistor with an additional 1000 ohms or so. Even without any change, you should be able to use that circuit to g .......
374: Tube DIY Asylum, RE: 45 amp cathode resistor explanation please. (0.00)
Posted by Paul Joppa on 2019-11-14, 15:56:02 (73.97.163.58)
You won't get 1.4 times the AC (unless the power supply is unloaded or the power transformer is HUGE!) - usually more like 1.1 to 1.2 times So maybe 325 volts would be typical. The RCA max spec is for .......
375: SET Asylum, RE: Need Help for Emission Labs 300B Mesh (0.00)
Posted by Paul Joppa on 2019-10-25, 11:47:07 (73.97.163.58)
I see more than 15 amps heater power, and that's just the diodes. And 730v above ground in the plate circuit. Seems excessive to me. Beyond those issues, it's too complicated for me to see by inspecti .......
376: SET Asylum, RE: Need Help for Emission Labs 300B Mesh (0.00)
Posted by Paul Joppa on 2019-10-24, 10:42:42 (73.97.163.58)
I calculate 5800 ohms; 5000 is close enough and readily available. Western Electric gives specifications in the data sheet for 4000 and 5500. My calculations are conservative relative to published val .......
377: Tube DIY Asylum, RE: more (0.00)
Posted by Paul Joppa on 2019-09-09, 21:02:21 (73.97.163.58)
Just a note - the old Svetlana data sheet for the 6N1P is in error. In the Russian data sheets, gm is 4.5mA/v and mu is 35, giving a plate resistance of about 7800 ohms. I agree about the 8.8Hz; I usu .......
378: Tube DIY Asylum, RE: Thanks triode (0.00)
Posted by Paul Joppa on 2019-09-04, 10:22:28 (73.97.163.58)
Oh, the variable part is not a problem - the necessary bleeder resistance depends on the choke inductance only - not on voltage or current draw. .......
379: Tube DIY Asylum, RE: Thanks triode (0.00)
Posted by Paul Joppa on 2019-09-03, 17:26:11 (73.97.163.58)
Traditionally, it was commonly recommended to use a large inductance with a low bleeder resistance, so that critical inductance is achieved with just the bleeder resistance. The bleeder will of course .......
380: Tube DIY Asylum, RE: 45 SET amps --- Upgrade Caps ? ............. (0.00)
Posted by Paul Joppa on 2019-07-31, 18:07:50 (73.97.163.58)
Really, replacing caps older than 10 years is recommended for electrolytic caps. I don't see any electrolytics in the photo. .......
381: SET Asylum, RE: Mainline (0.00)
Posted by Paul Joppa on 2019-07-25, 20:24:58 (73.97.163.58)
I still remember some audio club listening sessions more than 20 years ago, comparing small single-driver speakers. It was clear to many - certainly to me - that the paper cone speaker sounded like ca .......
382: SET Asylum, That has always been the intent ... (0.00)
Posted by Paul Joppa on 2019-07-24, 09:05:11 (108.72.1.210)
The S.E.X. amp (Single-Ended eXperimenter's) amp was from the beginning (~1996 IIRC) intended to be an affordable way to try out SET sound. It's gone through several major revisions over the years. Th .......
383: SET Asylum, RE: Dumb question (0.00)
Posted by Paul Joppa on 2019-07-16, 21:46:51 (73.97.163.58)
It is claimed that shunt regulators sound better than series regulators. I have not done the necessary experiments to determine for myself; the only place I can recall seeing reports of comparative li .......
384: Tube DIY Asylum, RE: ping Tre or Caucasian Black (0.00)
Posted by Paul Joppa on 2019-07-15, 14:45:56 (73.97.163.58)
Just checking - what is the input impedance of the power amp? The PAS-3 circuit really wants to see a high impedance; spec is 100K minimum. .......
385: SET Asylum, RE: Dumb question (0.00)
Posted by Paul Joppa on 2019-07-11, 20:41:53 (73.97.163.58)
I'll try to make a simple explanation: A basic filter is like an L-pad, in that there is a series element between the raw supply and the amplifier, and a shunt element in parallel with the amp. * exam .......
386: Tube DIY Asylum, RE: g2 regulation with zeners : schematic (0.00)
Posted by Paul Joppa on 2019-06-27, 09:55:35 (73.97.163.58)
The shunt regulator must carry more than the maximum G2 current (7mA on the data sheet at 250v plate, 250v screen). That makes the Zeners dissipate a lot of heat. .......
387: Tube DIY Asylum, RE: 26 v 76 (0.00)
Posted by Paul Joppa on 2019-06-19, 19:16:21 (73.97.163.58)
In most cases, the filamentary triodes of interest to us are more linear than the indirectly heated ones. I think this is more geometry than anything intrinsic to the cathode structure, but it does re .......
388: Tube DIY Asylum, RE: 27-71a design (0.00)
Posted by Paul Joppa on 2019-05-24, 11:29:37 (73.97.163.58)
Hammond makes an inexpensive 150-henry choke rated 8mA, RDC is 3700 ohms - looks like a reasonable substitute. The DCR of that choke is probably close enough; you can add 4K to the dropping resistor t .......
389: Tube DIY Asylum, RE: A reference! (0.00)
Posted by Paul Joppa on 2019-05-22, 16:59:58 (73.97.163.58)
Well, I think we both understand the same physics but are analyzing slightly different situations which leads to different-sounding conclusions. .......
390: Tube DIY Asylum, A reference! (0.00)
Posted by Paul Joppa on 2019-05-22, 11:22:09 (73.97.163.58)
The thread above, "audio transformer book," links a booklet by Crowhurst which discusses these issues on pp. 20-21. It's short and I just skimmed it, but the essential considerations seem to be descri .......
391: Tube DIY Asylum, RE: True for small signals, not for max power (0.00)
Posted by Paul Joppa on 2019-05-21, 12:19:41 (73.97.163.58)
I can't recall ever having seen such a treatment, which is probably why I derived this analysis myself. My purpose was to choose a saturation target for transformer design that corresponded to the tub .......
392: Tube DIY Asylum, yes and no (0.00)
Posted by Paul Joppa on 2019-05-20, 20:44:30 (73.97.163.58)
Start from a well-designed operating point - for instance, the one described in classic WE spec sheets for 300Bs, which is 300v plate to cathode, 60mA, and 3000 ohms load. It produces 6 watts. Suppose .......
393: Tube DIY Asylum, True for small signals, not for max power (0.00)
Posted by Paul Joppa on 2019-05-20, 17:14:02 (73.97.163.58)
Assuming the tube operating point is optimized for the target load impedance, the power bandwidth rolls off in the bass when the inductive reactance is equal to the nominal load impedance. I have some .......
394: High Efficiency Speaker Asylum, RE: Klipsch Cornwall mk3 special ed. (0.00)
Posted by Paul Joppa on 2019-05-08, 21:32:21 (73.97.163.58)
A number of people think the Cornwall has a particular affinity for SE 2A3 amps. (I've never lived with a Cornwall, so I remain agnostic personally.) If you haven't checked it out already, the Klipsch .......
395: Tube DIY Asylum, RE: Different tube in Ultrapath (0.00)
Posted by Paul Joppa on 2019-04-30, 00:02:13 (73.97.163.58)
Because the gain and transconductance are different between the tubes, the best way to determine bias is to look up the curves on a data sheet. I'll link the Raytheon data sheet; look at page 6. The 5 .......
396: Amp/Preamp Asylum, RE: Inherited amp (0.00)
Posted by Paul Joppa on 2019-04-20, 21:41:48 (73.97.163.58)
Hmmm... I see in the lower left what looks like some TO-220s, perhaps rectifiers. Some possibly red wires from the power transformer grommet down to that area supports that - sort of. So I'm guessing .......
397: Amp/Preamp Asylum, RE: Inherited amp (0.00)
Posted by Paul Joppa on 2019-04-20, 21:24:04 (73.97.163.58)
Well a hefty power transformer - 800vCT at 465mADC. Hammond 1650T in 1900 ohms CT, rated 120 watts. That's a start. Questions: any sign of solid-state or tube rectifiers? How about cathode bias resi .......
398: Tube DIY Asylum, RE: Miller Effect in Differential Amplifier Stage (0.00)
Posted by Paul Joppa on 2019-04-18, 21:53:38 (73.97.163.58)
Presumably, the diff amp has one grid grounded. So the capacitance from the other grid to ground would be the two capacitances in series - i.e. half the normal Miller capacitance of one stage in groun .......
399: Tube DIY Asylum, RE: Just checking that equation (0.00)
Posted by Paul Joppa on 2019-04-15, 12:25:03 (73.97.163.58)
You are right - I should have caught that one ... :^) If you do the calculation in ohms, then you get farads. If you use Kohms, then you get microfarads. .......
400: Tube DIY Asylum, RE: Just checking that equation (0.00)
Posted by Paul Joppa on 2019-04-14, 23:56:08 (73.97.163.58)
Yes your calculation is correct. As you can see, it's not useful for high load impedances - you can calculate the resonance between choke and cap to see where the cutoff is. It's way high with a 0.036 .......
401: Tube DIY Asylum, RE: Thanks Paul - very useful (0.00)
Posted by Paul Joppa on 2019-04-14, 12:11:20 (73.97.163.58)
The rule-of-thumb equation I use is 2 times inductance, divided by the load resistance squared. So both capacitance and inductance scale by the same factor, and so does the bass rolloff. .......
402: Tube DIY Asylum, RE: Here's the schematic (0.00)
Posted by Paul Joppa on 2019-04-13, 20:19:43 (73.97.163.58)
Given the 50-henry plate choke, I would encourage a simulation that takes more of the circuit into account. Specifically, for an 8Kohm load, you will get better performance with a 1.5uF cap. By using .......
403: Tube DIY Asylum, Holco Resistors ... (0.00)
Posted by Paul Joppa on 2019-04-09, 17:20:13 (73.97.163.58)
... were very popular for audio gear a couple decades ago; hadn't heard much about them more recently. These seem to be the HPF series, not the old H2 or H4 series (?) .......
404: Tube DIY Asylum, RE: individual bias push pull output (0.00)
Posted by Paul Joppa on 2019-04-06, 19:58:17 (73.97.163.58)
There are actually two issues - balancing the direct current in the two tubes, and measuring the total idle current. Williamson solved both problems with a resistor network. Hafler himself put small r .......
405: Tube DIY Asylum, RE: better bass, worse treble (0.00)
Posted by Paul Joppa on 2019-03-30, 19:04:44 (73.97.163.58)
Well, that's certainly different from my experience. .......
406: Tube DIY Asylum, better bass, worse treble (0.00)
Posted by Paul Joppa on 2019-03-30, 08:53:54 (73.97.163.58)
In an earlier post below, you said "If the low end rolloff is the result of insufficient inductance..." I just wanted to point out that if the high end rolloff is the result of too much leakage induct .......
407: Tube DIY Asylum, RE: What is the affect of lower B+ Voltage on a 300b Amplifier? (0.00)
Posted by Paul Joppa on 2019-03-27, 18:35:01 (73.97.163.58)
The available maximum power is proportional to the voltage squared - at least, to a first rough approximation. .......
408: Tube DIY Asylum, RE: thermistors in parallel? (0.00)
Posted by Paul Joppa on 2019-03-27, 18:32:07 (73.97.163.58)
More than that - the hotter one will have lower resistance (that's why you use them after all!) so it will hog the current - until it fails. .......
409: Tube DIY Asylum, RE: Grid leak bias (0.00)
Posted by Paul Joppa on 2019-03-25, 20:35:57 (73.97.163.58)
I looked up my old measurements - looks like about 10 years ago - and the Amperex 6DJ8 I measured would have about -1.1v bias in grid leak form, with a grid input resistance around 1 megohm - so fairl .......
410: Tube DIY Asylum, RE: Grid leak bias (0.00)
Posted by Paul Joppa on 2019-03-25, 20:18:43 (73.97.163.58)
My measurements of a couple 6DJ8s showed grid current starting around -800mV so no platinum grids there! It would be interesting to know the design history - probably never will though. .......
411: Tube DIY Asylum, RE: Grid leak bias (0.00)
Posted by Paul Joppa on 2019-03-25, 19:39:58 (73.97.163.58)
What are the tubes? If V2 has enough contact potential, it might work. Doesn't seem likely, though. .......
412: Tube DIY Asylum, RE: These ixys HiPerFREDTM Epitaxial Diode with soft recovery any good? (0.00)
Posted by Paul Joppa on 2019-03-23, 13:54:34 (73.97.163.58)
I think CB is talking about the Cree silicon carbide Schottky diodes, which are about USD 1 at 600v, and a bit over USD 2 for 1200v. .......
413: Tube DIY Asylum, RE: If you need a 60 amp part on a 300 volt AC they would be good (0.00)
Posted by Paul Joppa on 2019-03-22, 16:44:20 (73.97.163.58)
Some decades ago there was great enthusiasm for huge capacitor banks in solid-state amps. It was thought to be a superior alternative, or at least a cheaper one, to regulated power supplies. The enthu .......
414: Tube DIY Asylum, RE: Schottky Diode Question (0.00)
Posted by Paul Joppa on 2019-03-18, 14:50:18 (73.97.163.58)
For clarity, ultra fast, soft recovery diodes are readily available up to 1000 volts in axial form and made from silicon. They are not Schottky diodes. Schottky diodes have no recovery spike at all. T .......
415: Tube DIY Asylum, RE: Understanding MC275 power supply (0.00)
Posted by Paul Joppa on 2019-03-08, 13:21:55 (73.97.163.58)
It's a standard fullwave bridge bipolar power supply, with the negative output grounded instead of the usual center-tap grounded. Usually such designs will have all the caps duplicated on the positive .......
416: Tube DIY Asylum, RE: Choke Inductance (0.00)
Posted by Paul Joppa on 2019-03-05, 20:44:46 (73.97.163.58)
If the two coils had separate cores, your math would be correct. But they share the same core, so they are not independent inductors. However, you made me think some more. I was wrong about the curren .......
417: High Efficiency Speaker Asylum, Sweet Sixteen? (0.00)
Posted by Paul Joppa on 2019-03-05, 20:04:08 (73.97.163.58)
Well, consider the source - the technical understanding available from the pages of Poptronics was pretty low in general. Does anyone else remember the very popular Sweet Sixteen? I'll link the articl .......
418: Tube DIY Asylum, RE: Series Grounding (0.00)
Posted by Paul Joppa on 2019-03-05, 14:38:11 (73.97.163.58)
Looks good! Magnequest Mike has been handling some changes in his life the last few years, but as far as I know he has not dropped out. He's hinted at some new production - I can't remember where I sa .......
419: High Efficiency Speaker Asylum, RE: "The Mellow Monster" Popular Electronics' 1962 version of H.F. Olson - Frank Massa 's Compound horn (0.00)
Posted by Paul Joppa on 2019-03-05, 13:58:55 (73.97.163.58)
When I was in high school, a friend of my father's built one. Construction was in our basement, so I saw some of the process - it took a few weeks - quite a complicated build! The next year (IIRC) th .......
420: Tube DIY Asylum, RE: Series Grounding (0.00)
Posted by Paul Joppa on 2019-03-04, 21:05:24 (73.97.163.58)
A two-star ground - that's cool! It should work well. A few other points: * The XLR "ground" is actually a shield, and is properly connected to the chassis near the socket, not to the signal ground. .......
421: Tube DIY Asylum, RE: Kelvin Capacitors and Grounding (0.00)
Posted by Paul Joppa on 2019-03-04, 13:50:41 (73.97.163.58)
You have understood my post accurately, in spite of my poor articulation of it! But see also mu reply to Triode Kingdom - star grounds are also a viable approach, which I failed to be clear about. ::: .......
422: Tube DIY Asylum, RE: Kelvin Capacitors and Grounding (0.00)
Posted by Paul Joppa on 2019-03-04, 13:42:51 (73.97.163.58)
No, it was not personal. Star grounding as you described it is a viable alternative. As is always the case, any good idea can fail through poor implementation, and most can succeed with careful imple .......
423: Tube DIY Asylum, RE: Kelvin Capacitors and Grounding (0.00)
Posted by Paul Joppa on 2019-03-03, 20:19:05 (73.97.163.58)
The principle at work is that any fluctuating current in a signal-ground wire will drop a small voltage because its resistance is not quite zero. So the best place for a ground reference is nearest th .......
424: Tube DIY Asylum, Yes there are special considerations (0.00)
Posted by Paul Joppa on 2019-03-01, 14:40:24 (73.97.163.58)
Wikipedia has an informative summary article - I'll link it. Read the first three sections especially. Note this article does not cover creepage. Discharges - sparks, creepage, coronas, and arcs - gen .......
425: High Efficiency Speaker Asylum, the Bullet ... (0.00)
Posted by Paul Joppa on 2019-02-05, 16:38:48 (73.97.163.58)
... they don't call it the "earburner" for nothing! To be fair, it did improve the sound of a D130 the one time I tried it. Not by enough to ever want to hear it again, though! .......
426: Tube DIY Asylum, RE: Thermal/Grid Noise - 12AX7 VS 6N2P? (0.00)
Posted by Paul Joppa on 2019-02-04, 11:12:24 (73.97.163.58)
Flicker noise is more related to the cathode coating and material purity, so it has more to do with manufacturing than tube type. That said, often an unused tube will become quieter (with respect to 1 .......
427: High Efficiency Speaker Asylum, RE: Suggestions For Implementation Of EV LS-8 (0.00)
Posted by Paul Joppa on 2019-02-04, 10:58:47 (73.97.163.58)
Good point! I didn't even think about t-lines, but that has good potential for this driver. .......
428: High Efficiency Speaker Asylum, RE: Suggestions For Implementation Of EV LS-8 (0.00)
Posted by Paul Joppa on 2019-02-03, 16:39:50 (73.97.163.58)
Google led me to the link below; scroll down a few posts for some measured parameters. QT is in the range 1.0-1.2, which is pretty high. A Chebyshev alignment might be possible but would call for a mu .......
429: High Efficiency Speaker Asylum, RE: Semantics? Not. (0.00)
Posted by Paul Joppa on 2019-01-25, 16:17:42 (73.97.163.58)
While I agree that "fullrange driver" is imprecise, I don't know a better word to suggest a driver suitable for a single-driver system. I think the term is often used in that sense - in other words, a .......
430: Tube DIY Asylum, RE: RCA Phono Preamp (0.00)
Posted by Paul Joppa on 2019-01-21, 17:38:56 (73.97.163.58)
6SC7 is definitely in RC-15, RC-16, RC-17, and RC-18, and there is no magnetic-cartridge preamp at all in RC-14. I have that same vague memory of 6SL7, but we must both be mistaken. Wishful thinking? .......
431: Tube DIY Asylum, RE: RCA Phono Preamp (0.00)
Posted by Paul Joppa on 2019-01-21, 17:20:43 (73.97.163.58)
Until 1959, the RCA manuals had the 6SC7 circuit with an older, non-RIAA equalization. RCA introduced the New Orthophonic (same as RIAA) equalization in 1953 - I have to suppose they waited until ther .......
432: Tube DIY Asylum, RE: RCA Phono Preamp (0.00)
Posted by Paul Joppa on 2019-01-21, 11:14:42 (73.97.163.58)
Yes, that's why I posted the link. Without the 180pF, what remains is a pretty good RIAA passive equalizer, and has all the poles and zeros specified. The extra pole produced by that 180pF cap cannot .......
433: Tube DIY Asylum, RE: RCA Phono Preamp (0.00)
Posted by Paul Joppa on 2019-01-20, 21:48:30 (73.97.163.58)
With respect to gain, the discussion at the bottom of the posted circuit gives a gain of 150 (43.52dB) but the note just under the circuit itself gives 550mV/3mV, or 183 (45.26dB). Plus, the circuit s .......
434: Tube DIY Asylum, RE: How would you implement them? (0.00)
Posted by Paul Joppa on 2019-01-08, 12:56:19 (73.97.163.58)
Grid chokes are often used with SE power tubes, between grid and ground - replacing the usual grid-to-ground resistor (usually 250K-500Kohms). They provide a more rapid recovery from a transient overl .......
435: Tube DIY Asylum, Grid choke? (nt) (0.00)
Posted by Paul Joppa on 2019-01-06, 19:49:51 (73.97.163.58)
nt .......
436: Tube DIY Asylum, RE: Miller Effect (0.00)
Posted by Paul Joppa on 2019-01-03, 07:58:06 (73.97.163.58)
250K? Well, there's your problem! I try to never use pots over 100K for just this reason. .......
437: Tube DIY Asylum, expanded notes (0.00)
Posted by Paul Joppa on 2018-12-30, 14:50:00 (73.97.163.58)
There are at least two things going on, one on each side of the diaphragm. If the driver is in a sealed box, then the spring constant is slightly nonlinear, and an undistorted speaker motor will still .......
438: Tube DIY Asylum, RE: The single-ended nature of air !!! (0.00)
Posted by Paul Joppa on 2018-12-30, 14:32:25 (73.97.163.58)
Class C is cut off for more than half the cycle, B is half the cycle, and AB is less than half a cycle. The trick is to define "cut off" in a meaningful way with tubes, which have a soft cutoff. To m .......
439: Tube DIY Asylum, RE: The single-ended nature of air !!! (0.00)
Posted by Paul Joppa on 2018-12-29, 21:19:50 (73.97.163.58)
It happens in horns as well. I first saw this in Leo Beranek's classic "Acoustics." .......
440: Tube DIY Asylum, RE: The single-ended nature of air !!! (0.00)
Posted by Paul Joppa on 2018-12-29, 21:16:46 (73.97.163.58)
Just a note on Class A SETs - some designers use a lower-than-normal transformer impedance, which produces more power but at the cost of increased distortion. If you push this too far, it looks more a .......
441: Tube DIY Asylum, RE: Wow, did I break the forum? (0.00)
Posted by Paul Joppa on 2018-12-28, 17:20:08 (73.97.163.58)
The transconductance usually refers to plate current per volt of grid bias, which will be somewhat less than the plate+screen current. Here's Spangenberg: "... the control-grid-plate transconductance .......
442: Tube DIY Asylum, RE: Help and recommendations for feedback in SE UL amp (0.00)
Posted by Paul Joppa on 2018-12-26, 19:53:55 (73.97.163.58)
The circuit you show creates a low-impedance point at the second-stage grid, which is not a low-distortion load for the first stage. You can replace the 2.5v bias of the first stage with a resistor, a .......
443: Tube DIY Asylum, RE: Amp circuit? Plate impedance calculation. (0.00)
Posted by Paul Joppa on 2018-12-26, 16:45:55 (73.97.163.58)
"It's complicated!" Eli estimated a 3000 ohm transformer primary (end to end). To get 60 watts would need 425vRMS or 600v peak to peak across the primary. With the primary center-tap at B+, each tube .......
444: Tube DIY Asylum, 5842 for transconductance NT (0.00)
Posted by Paul Joppa on 2018-12-25, 19:47:56 (73.97.163.58)
no text .......
445: High Efficiency Speaker Asylum, RE: update.... (0.00)
Posted by Paul Joppa on 2018-12-25, 19:41:42 (73.97.163.58)
An alternative is to put the driver in a sealed box, sized to get a Q of 0.5 for Linkwitz-Riley second order. Many sub amps will have a suitable second-order lowpass function for the woofer. This way, .......
446: Tube DIY Asylum, RE: Partition Noise (0.00)
Posted by Paul Joppa on 2018-12-18, 10:34:25 (73.97.163.58)
I have the same intuition - that the partition noise current at the plate is identical to and out of phase with that at the screen grid, and thus they would exactly cancel when triode-wired. In face, .......
447: Tube DIY Asylum, RE: Partition Noise (0.00)
Posted by Paul Joppa on 2018-12-17, 17:28:05 (73.97.163.58)
"... typically [partition noise] makes a given pentode 6dB to 14dB noisier than that pentode connected as a triode." Morgan Jones, "Valve Amplifiers" 2nd edition, page 90. .......
448: High Efficiency Speaker Asylum, Maybe a LOT of x-max .... (0.00)
Posted by Paul Joppa on 2018-12-15, 21:24:20 (73.97.163.58)
Having played with the nearly identical FE167 a little myself, I think it's mostly the xmax limitation. I put them in a large box (one cubic foot, IIRC) tuned low (again, 45-50Hz IIRC) to optimize for .......
449: SET Asylum, RE: Input sensitivity (0.00)
Posted by Paul Joppa on 2018-12-12, 18:15:44 (73.97.163.58)
The situation with gain standards has never been simple, and does not seem to be getting better. :^) More than a decade ago, I wrote a "white paper" on the subject. It's more than anyone really wants .......
450: Tube DIY Asylum, A little more (0.00)
Posted by Paul Joppa on 2018-12-08, 15:51:50 (73.97.163.58)
This question intrigued me enough to look for a bit more information, which I found in the 1962 RCA book "Electron Tube Design." There's 28 pages on heaters! Lifetime of the heater-cathode insulation .......
451: Tube DIY Asylum, RE: Cathode Followers & Non-Elevated Heaters (0.00)
Posted by Paul Joppa on 2018-12-08, 11:07:08 (73.97.163.58)
For what it's worth, there are two mechanisms involved in heater-cathode leakage. The first is simple voltage breakdown of the insulation, which sets an absolute maximum voltage. The other is electro .......
452: Tube DIY Asylum, RE: Heater Wiring? (0.00)
Posted by Paul Joppa on 2018-12-04, 21:22:37 (73.97.163.58)
For these low-voltage filaments, the purpose of twisting is to reduce the magnetic field generated by the high current. The electric field is small due to the low voltage. So the analysis is simple. W .......
453: High Efficiency Speaker Asylum, RE: When Calculating BSC Using An Online Calculator (0.00)
Posted by Paul Joppa on 2018-11-05, 13:21:25 (73.97.163.58)
The BSC filter is designed on the assumption that it drives a load of constant resistance. With a speaker-level BSC, the higher frequencies are attenuated, and the increasing impedance of the driver a .......
454: High Efficiency Speaker Asylum, RE: Hard, honky horn speakers (0.00)
Posted by Paul Joppa on 2018-11-05, 13:14:01 (73.97.163.58)
Some knowledgeable people think it's the resonances within the horn that cause this effect. These are mostly axial resonances caused by reflections at the mouth back into the horn. These are sometimes .......
455: Tube DIY Asylum, RE: need help with understanding a table (0.00)
Posted by Paul Joppa on 2018-11-04, 20:42:55 (73.97.163.58)
This circuit is operating the 2A3s in deep Class A, so 2.5K each or 5K end-to-end is appropriate. The operating point is 250v plate to cathode, with ~20v dropped in the OPT windings and ~50v across th .......
456: High Efficiency Speaker Asylum, RE: EV LS-8 Open Baffle Test Cabinet (0.00)
Posted by Paul Joppa on 2018-10-30, 18:40:37 (73.97.163.58)
I'm loving this project! My first "hifi" started with a speaker, built by a friend of my fathers when I was in high school. That speaker was the "Mello Monster" from popular Electronics, October 1962. .......
457: SET Asylum, RE: Speaking of KVs...building a HV power supply. (0.00)
Posted by Paul Joppa on 2018-09-29, 01:46:52 (176.92.108.94)
Find an old copy of the ARRL ham radio handbook, from the fifties or sixties. Modern safety standards are much more stringent, of course, but those books cover the practical details very well, at the .......
458: High Efficiency Speaker Asylum, RE: you'll get an estimate of sensitivity, not efficieny with such data (0.00)
Posted by Paul Joppa on 2018-09-29, 01:38:41 (176.92.108.94)
The reference distance of 1 meter assumes the source is effectively a point source, i.e. much smaller than one meter. (10% is often used as a definition of "much smaller"). Obviously your woofer syste .......
459: Tube DIY Asylum, RE: Tips for Preparing Coax? (0.00)
Posted by Paul Joppa on 2018-09-24, 21:58:05 (176.92.108.94)
The traditional way is to pry open a spot on the braid and pull the center wire out through that hole. That leaves the braid intact, making it easy to solder. .......
460: Tube DIY Asylum, RE: Curious and confused..tube amp run only attached to speakers.. (0.00)
Posted by Paul Joppa on 2018-09-08, 19:09:11 (73.97.163.58)
There are two things going on here; both are mostly only a problem with pentodes. As Triode Kingdom said, severe overdrive will produce excessive voltages, as the OPT inductive energy confronts a cuto .......
461: High Efficiency Speaker Asylum, RE: High efficient surround speakers? (0.00)
Posted by Paul Joppa on 2018-09-08, 18:55:15 (73.97.163.58)
If I recall correctly, the official requirements for frequency response are not at all difficult - something like 100-5000Hz is considered adequate. There are many wide-range drivers in the 6" to 8" r .......
462: Tube DIY Asylum, RE: KT150 subsisute KT88 (0.00)
Posted by Paul Joppa on 2018-09-08, 14:58:15 (73.97.163.58)
Not enough information is given in the data sheet to answer the question. The only operating point shown (single-ended pentode mode 400v/225v) has the same output power as a 6550 at the same voltages, .......
463: SET Asylum, RE: SET's in push-pull config (0.00)
Posted by Paul Joppa on 2018-09-03, 12:38:27 (73.97.163.58)
SET stands for Single-Ended Triode, so when two triodes are in push-pull, they lose all of the single-ended magic and none of the triode magic. That is of course over-simplified :^) Here are a few oth .......
464: High Efficiency Speaker Asylum, RE: Beaming (0.00)
Posted by Paul Joppa on 2018-09-02, 16:06:03 (73.97.163.58)
To a listener, beaming is not, by itself, an undesirable attribute. It's mostly a problem for theoreticians because it calls for a much more complicated analysis, and theoreticians (I am one) are basi .......
465: Tube DIY Asylum, RE: What effect does a Lower B+ Voltage Have ? (Welborne Laurel 300B amp)............ (0.00)
Posted by Paul Joppa on 2018-08-27, 12:21:03 (73.97.163.58)
It's mostly just the power, which drops as the square of voltage ratio (first approximation). .......
466: Tube DIY Asylum, A Y cable will short L and R together ... (0.00)
Posted by Paul Joppa on 2018-08-15, 22:11:23 (73.97.163.58)
... which will make all the outputs mono, and the difference signal may demand excess current from the preamp output, causing distortion. Resistive mixers are simple, but they will produce crosstalk i .......
467: SET Asylum, RE: WE91 question (0.00)
Posted by Paul Joppa on 2018-08-10, 19:46:41 (73.97.163.58)
awsjr is correct. As I understand it from a phone conversation I had with Mike a few years ago, the PGP8 was derived from one of Mike's many historical design records, possibly from Freed (?). The ori .......
468: SET Asylum, RE: WE91 question (0.00)
Posted by Paul Joppa on 2018-08-06, 16:47:19 (73.97.163.58)
That draft design is now 6 years old; here are a couple notes: * The 300B filament power rectifiers may produce not quite the desired 5.0 volts - it mostly depends on what your powerline voltage is. A .......
469: High Efficiency Speaker Asylum, RE: That's for the horn-loaded model (0.00)
Posted by Paul Joppa on 2018-07-29, 14:35:20 (73.97.163.58)
According to our measurements, the sensitivity claim is pretty accurate, on axis and over the 3kHz-10kHz range. .......
470: SET Asylum, RE: output transformer recommendation (0.00)
Posted by Paul Joppa on 2018-07-28, 23:29:26 (73.97.163.58)
To be fair, there are some aspects of audio transformer design in which you must trade off better measurements against better sound. If you publish specs, people will judge by comparing specs, since t .......
471: MagneQuest/Peerless Forum, RE: 211 Works Well Also... (0.00)
Posted by Paul Joppa on 2018-07-24, 17:19:02 (73.97.163.58)
Here's a little background, while we wait for Mike to chime in. The FS-100PF was a special parafeed version. The core is a slightly shorter stack than the original series feed version. There are some .......
472: Tube DIY Asylum, RE: Okay, this isnt funny (0.00)
Posted by Paul Joppa on 2018-06-28, 18:29:13 (73.97.163.58)
That's like saying "the proper tire pressure for a car is 1.0% of the car's weight." It sounds like a fact, but it's just hot air. There are a range of operating conditions that work well; the choice .......
473: MagneQuest/Peerless Forum, RE: FS-100 PF and GM70 and 845 amp DIYers (0.00)
Posted by Paul Joppa on 2018-06-20, 13:15:25 (73.97.163.58)
The main issue is, as you noted, the high voltage. My advice is to make sure that everything - even the hookup wire! - must be rated for the voltage to which is it connected. It is, again as noted, ve .......
474: SET Asylum, RE: Opinion on PA1502A headphone amp?? (0.00)
Posted by Paul Joppa on 2018-06-09, 18:20:48 (73.97.163.58)
*** Edit: CB posted while I was typing, so there's some overlap. *** In the linked diagram, the 6P6P screen grid (middle grid) is connected to B+ (179 volts). It is operating as a pentode. In triode m .......
475: Tube DIY Asylum, RE: 45 SET with high pass filtering (0.00)
Posted by Paul Joppa on 2018-06-05, 15:10:01 (73.97.163.58)
Complete accident - wish I HAD done it on purpose! .......
476: Tube DIY Asylum, RE: 45 SET with high pass filtering (0.00)
Posted by Paul Joppa on 2018-06-04, 20:06:31 (73.97.163.58)
* 8nF sounds good - 8.2 is readily available, and insignificantly different for a first-order filter like this one. * The coupling and bypass caps are designed with a hefty margin; as you said, they a .......
477: Tube DIY Asylum, RE: what to do, what to do..... (0.00)
Posted by Paul Joppa on 2018-06-04, 09:06:11 (73.97.163.58)
The 71A has a plate resistance similar to the 45, and I have heard a very successful 45 amp using the TFA-2004 which is also a 3000 ohm output transformer. Damping factor is a little on the low side, .......
478: Tube DIY Asylum, RE: what to do, what to do..... (0.00)
Posted by Paul Joppa on 2018-06-03, 21:47:13 (73.97.163.58)
My suggestion would be an ordinary switch, rated for power-line voltage, but only activate it when the amp is unpowered and the caps have discharged. You won't easily find a switch rated for more than .......
479: Tube DIY Asylum, RE: 45 SET with high pass filtering (0.00)
Posted by Paul Joppa on 2018-06-03, 21:27:06 (73.97.163.58)
Are you suggesting to change the parafeed cap? That will NOT remove bass from the 45 or the driver (6072?) - it basically works the same as a cap in series with the speaker. (It will still reduce con .......
480: Tube DIY Asylum, RE: Japanese power transformers in the US? (0.00)
Posted by Paul Joppa on 2018-06-01, 18:16:30 (73.97.163.58)
More than that, actually. When I design power transformers for commercial products, I keep the flux quite low - around 10kGauss at 60Hz. So the flux at 50Hz is 12kGauss. Typical "cost-effective" power .......
481: Tube DIY Asylum, RE: Japanese power transformers in the US? (0.00)
Posted by Paul Joppa on 2018-05-31, 23:07:14 (73.97.163.58)
A 100v/50Hz transformer will have the same magnetic flux when used at 120v/60Hz - the core won't saturate. Of course the secondary voltages will also be 20% higher. If there is a high voltage secondar .......
482: Tube DIY Asylum, RE: If I said it once I've said it a thousand times (0.00)
Posted by Paul Joppa on 2018-05-30, 22:06:15 (73.97.163.58)
The math is correct, it just does not apply to selecting a fuse (as said by Johno above). The right fuse is the smallest one that will not blow in normal use when the amp is operating as designed. Usu .......
483: Tube DIY Asylum, RE: Theory vs practice (0.00)
Posted by Paul Joppa on 2018-05-29, 13:51:01 (73.97.163.58)
The Red Bible, Radiotron Designer's Handbook 4th edition (RDH4) says on page 92 near the top "...it is very important that these resistors be non-inductive..." This is the only reference I could find .......
484: Tube DIY Asylum, RE: Theory vs practice (0.00)
Posted by Paul Joppa on 2018-05-28, 20:40:17 (73.97.163.58)
"Try it and see" is always a good starting point. For small values - say, under 1000 ohms - I have it on reliable authority that metal film and carbon film work well enough. I would be uncomfortable a .......
485: Tube DIY Asylum, RE: input transformer (0.00)
Posted by Paul Joppa on 2018-05-28, 20:27:50 (73.97.163.58)
Some step-up transformers have secondary resonances around their high-frequency limit, which are optimall damped when loaded with the design load impedance. I would not expect this to be an issue at 6 .......
486: Tube DIY Asylum, RE: LCR meters (0.00)
Posted by Paul Joppa on 2018-05-28, 20:20:04 (73.97.163.58)
I have absolutely no relevant data to quote. But I did have a career as an engineer, so I almost always have a semi-educated guess. In this case (FWIW, which ain't much) it's that you have about an 80 .......
487: SET Asylum, RE: input sensitivity of Fi 2a3 monos amp (0.00)
Posted by Paul Joppa on 2018-05-28, 20:14:57 (73.97.163.58)
I don't know any measurements, but the 6SF5 driver has a mu of 100, so a gain of 70 seems reasonable. Since the 2A3 needs some 32 volts rms to achieve full power, I'd guess the input sensitivity to be .......
488: Tube DIY Asylum, Seconded (0.00)
Posted by Paul Joppa on 2018-05-27, 20:52:18 (73.97.163.58)
Good point, Dave! .......
489: Tube DIY Asylum, RE: LCR meters (0.00)
Posted by Paul Joppa on 2018-05-27, 17:26:12 (73.97.163.58)
Others have mentioned the importance of DC. I'll just add two more considerations: * Such meters usually use a higher frequency, like 1000Hz or more. Inductance in iron-core chokes is a function of fr .......
490: Tube DIY Asylum, RE: DC and transformer coupling?? (0.00)
Posted by Paul Joppa on 2018-05-23, 11:43:27 (73.97.163.58)
In olden times, it was not uncommon for turntables to wind up with a low tonearm resonance, which can make a large signal at 5-10Hz. Even without that, a warped record can produce a very large very lo .......
491: Tube DIY Asylum, RE: Would you use these chokes? (0.00)
Posted by Paul Joppa on 2018-05-09, 12:02:52 (73.97.163.58)
The link says 10H center-tapped, or 2x5H. This makes no sense. If there are two identical windings in series they would have 4 times the inductance, not 2 times. And the separate windings are not inde .......
492: Tube DIY Asylum, CDE guidance (0.00)
Posted by Paul Joppa on 2018-05-07, 20:18:18 (73.97.163.58)
Cornell-Dubilier has a 20-page "Aluminum Electrolytic Capacitor Application Guide," which includes an interesting graph of leakage vs. voltage. It shows the leakage current increasing as approximately .......
493: Tube DIY Asylum, RE: oh boy... (0.00)
Posted by Paul Joppa on 2018-05-06, 15:52:43 (73.97.163.58)
The problem as presented is still that the evidence (exploding/overheating caps) is characteristic of a cap installed backwards, while the connection is said to be in the correct direction. The photo .......
494: High Efficiency Speaker Asylum, RE: I agree with Bill (0.00)
Posted by Paul Joppa on 2018-04-24, 18:19:30 (73.97.163.58)
Interesting! Thanks for the feedback. I suppose the foam does not have enough shear stiffness to work well in that application. .......
495: High Efficiency Speaker Asylum, I agree with Bill (0.00)
Posted by Paul Joppa on 2018-04-23, 21:37:22 (73.181.211.24)
Dan "Doc Bottlehead" did some experimenting with the foam board in the late nineties; it's really way too flexible below resonance and too low in mass above resonance to be much of a barrier. Also the .......
496: Tube DIY Asylum, RE: All input levels (0.00)
Posted by Paul Joppa on 2018-04-11, 11:42:55 (73.181.211.24)
I remember a class I took, 2 or 3 decades ago, on design of experiments. The best thing I took from it was to assume the first experiment or two will fail to work for unanticipated reasons. Eventually .......
497: Tube DIY Asylum, RE: All input levels (0.00)
Posted by Paul Joppa on 2018-04-10, 18:24:46 (73.181.211.24)
Looking more carefully at my numbers, I find some oddities in my spreadsheet calculations - well, it was nearly 20 years ago! Anyhow, thanks for the feedback - I'll edit my previous post. Apparently I .......
498: Tube DIY Asylum, RE: All input levels (0.00)
Posted by Paul Joppa on 2018-04-09, 21:01:41 (73.181.211.24)
EDITED: This post has erroneous numbers (see my reply to Dave, two posts below). I'll add some ***notes*** but otherwise leave the incorrect text so Dave's post makes sense. I dug up my old measuremen .......
499: Tube DIY Asylum, RE: 6SN7 maximum ratings ... (0.00)
Posted by Paul Joppa on 2018-04-09, 17:58:23 (73.181.211.24)
Just a note - it's only the 6SN7-GTA and 6SN7-GTB that have the 7.5 watt envelope power rating - the older 6SN7-GT is rated 5 watts total. .......
500: Tube DIY Asylum, RE: RCA phono stage question (0.00)
Posted by Paul Joppa on 2018-04-08, 16:48:35 (73.181.211.24)
You can correct the series resistance for the second stage input impedance (grid resistor) as well as the first stage source impedance. This is valid independent of the other equalization components. .......
Found total of 500 records, Query: , Author: Paul Joppa in All Forums, Time: 3 sec.