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1: Tube DIY Asylum, RE: Is it a Bad Tube or a Bad fuse (Fuse Fatigue)? (0.00)
Posted by trobbins on 2024-02-27, 14:34:35 (167.179.137.188)
Caveat emptor - if you want to operate a tube amp then there is always a chance you have to pay for service, or do it yourself. No harm in pondering possible fault scenarios, but if you can't progress .......
2: Tube DIY Asylum, RE: Modification of a Heath W5-M - Help and advice (0.00)
Posted by trobbins on 2024-01-05, 22:59:45 (167.179.137.188)
Imho, you could follow your initial aim if you could mitigate known risks, and prepare predesign and fault protection that would further mitigate risks. If you could beg/borrow/hire suitable insulatio .......
3: Tube DIY Asylum, RE: Bringing down the ripple......? (0.00)
Posted by trobbins on 2023-07-22, 19:52:41 (167.179.190.55)
I was able to just measure some 'signature' noise related to 1N4007 rectification, and that required a very low noise floor spectrum with an EMU0404. The noise originates from the transformer winding, .......
4: Tube DIY Asylum, RE: Here's the chart you ask for (0.00)
Posted by trobbins on 2023-07-21, 02:07:58 (167.179.190.55)
Perhaps best not to dictate what this forum is for. From the posting rules - What you can post: You can post anything relevant to the world of audio, music, video and home theater. Remember to place y .......
5: Tube DIY Asylum, RE: Here's the chart you ask for (0.00)
Posted by trobbins on 2023-07-19, 17:55:27 (1.146.107.200)
Tre is correctly describing how to interpret valve diode data sheets. I will happily reiterate that any identification of a max capacitance is related to preset conditions. What dictates any capacitan .......
6: Tube DIY Asylum, RE: Bringing down the ripple......? (0.00)
Posted by trobbins on 2023-07-14, 00:03:18 (167.179.137.188)
(1) Note that the ss diodes make the bottom half of a bridge rectifier - which is totally fine, as the valve diodes soften the turn-off transitions and there is no 'fighting' or extra artifacts in tha .......
7: Tube DIY Asylum, RE: How much AC ripple is acceptable in a SE PSU? (0.00)
Posted by trobbins on 2023-07-13, 16:37:37 (167.179.137.188)
You say you prefer the smaller cap size alternative, and that you use your ears for assessment, but you say nothing about what you hear regarding the ripple/hum ?? If your aim is to hear no audible h .......
8: Tube DIY Asylum, RE: Partridge design from Mercury Magnetics (0.00)
Posted by trobbins on 2023-06-06, 17:00:53 (167.179.137.188)
Partridge model TG7549 and later TH7549 are the HiWatt 100W DR103 output transformers - is that what you didn't know? Perhaps see https://hiwatt.org/tech2.html . .......
9: Tube DIY Asylum, RE: Partridge design from Mercury Magnetics (0.00)
Posted by trobbins on 2023-06-05, 05:43:24 (167.179.137.188)
Ta, that response is more likely. That is the magnitude response of frequency, not the phase response (which would likely better show where the typical resonance starts at circa 60-70kHz). Do you reca .......
10: Tube DIY Asylum, RE: Partridge design from Mercury Magnetics (0.00)
Posted by trobbins on 2023-06-05, 01:34:12 (167.179.137.188)
I'll assume you meant that you had measured frequency response (as impedance response would not have been flat). I'll also assume you meant that the frequency response magnitude was flat (as it would .......
11: Tube DIY Asylum, RE: Partridge design from Mercury Magnetics (0.00)
Posted by trobbins on 2023-06-04, 16:37:28 (167.179.137.188)
"I have a pair of them (for sale in fact)" - is 'for sale' the reason for a strident response? Have you measured your transformers of impedance (magnitude and phase) in the audio range and at least to .......
12: Tube DIY Asylum, RE: Partridge design from Mercury Magnetics (0.00)
Posted by trobbins on 2023-06-04, 05:00:27 (167.179.137.188)
Partridge ended making transformers for HiWatt in 1981, and had supplied SoundCity into the mid-1970s. Partridge were getting too expensive and were getting into financial difficulty, and the company .......
13: Tube DIY Asylum, RE: Schottky has "no" recovery (0.00)
Posted by trobbins on 2022-11-15, 19:13:49 (167.179.137.188)
Likely need much more than a scope. I used a soundcard spectrum analyser to try and identify any noise up to 90kHz for a ss diode B+ supply, and could 'just' discern some signal related to the PT seco .......
14: Tube DIY Asylum, RE: Energy prices out of control may put at risk tube amplifiers (0.00)
Posted by trobbins on 2022-11-06, 21:37:20 (167.179.137.188)
Let's be realistic here, most people are happy to pay many many dollars for valve equipment, and then for swapping out output stage valves every few thousand hours. Perhaps do a total life-cycle cost .......
15: Tube DIY Asylum, RE: Measuring Arbitrary Waveforms (0.00)
Posted by trobbins on 2022-09-09, 15:35:19 (167.179.137.188)
Yes the optical measurement technique seems quite practical as those valves give a good opportunity for accessing the heater illumination. The old vintage method (Disappearing Filament Pyrometer) was .......
16: Tube DIY Asylum, RE: Measuring Arbitrary Waveforms (0.00)
Posted by trobbins on 2022-09-07, 17:25:32 (167.179.137.188)
The HP3400 is a great meter for your application, as there are few other meters that go beyond a few hundred kHz bandwidth, but it seems you don't have a 3400 for starters (or one that is in cal)? You .......
17: Tube DIY Asylum, RE: Old Wiring (0.00)
Posted by trobbins on 2022-08-12, 00:32:38 (167.179.137.188)
That sounds typical of some vintage gear I've come across - especially prior to to 1950'ish. One of the risks of restoration that makes it a labour of love, not $ remuneration. .......
18: Tube DIY Asylum, RE: Great, thank you. (0.00)
Posted by trobbins on 2022-07-23, 19:05:34 (167.179.137.188)
Were you thinking about: - adding two series connected 1N4007 diodes in series with each anode of V5. - adding say a 4k7 0.5-1W resistor from one end of the 300 ohm bias adjust pot to ground. - matchi .......
19: Tube DIY Asylum, RE: 6L6GC screens in Heathkit W5m amps. (0.00)
Posted by trobbins on 2022-07-23, 17:44:01 (167.179.137.188)
Pete, the datasheet for 6L6GC indicates a 500V screen is acceptable for UL connection. Note that 500V is the screen voltage minus the cathode voltage for the W5M, so your amp would idle the 6L6GC's sc .......
20: Tube DIY Asylum, RE: 6L6GC screens in Heathkit W5m amps. (0.00)
Posted by trobbins on 2022-07-23, 16:04:46 (167.179.137.188)
Pete, are you asking questions because you have tried to interpret datasheet details and can see an inconsistency, or because you have no technical awareness of those queries and are just asking to ga .......
21: Tube DIY Asylum, RE: interesting read on cap input vs choke input (0.00)
Posted by trobbins on 2022-05-18, 16:53:33 (167.179.137.188)
The article elaborates on the region of operation where wCR is small (which wasn't adequately modelled by Schade). For typical valve amp power supplies the wCR is approaching 100 (ie. at or above the .......
22: Tube DIY Asylum, RE: interesting read on cap input vs choke input (0.00)
Posted by trobbins on 2022-05-17, 20:29:19 (167.179.137.188)
As Tom indicates, the article is about transformer leakage inductance in large kVA applications. That is a concern for diode and scr rectification as those devices are quite slow, and glitches occur, .......
23: Tube DIY Asylum, RE: Can choke be used for power voltage regulation ? (0.00)
Posted by trobbins on 2022-05-13, 15:06:39 (167.179.137.188)
In addition, note that if the load current doesn't vary much, then the voltage is inherently regulated, and a reduction in ripple becomes much more influential. You can use PSUD2 to assess the influen .......
24: Tube DIY Asylum, RE: Thermal runaway? (0.00)
Posted by trobbins on 2022-05-11, 17:20:54 (167.179.137.188)
Did you confirm that the fault moved with a particular tube, or always occurred at the same location no matter what tube was in there? .......
25: Tube DIY Asylum, RE: Thermal runaway? (0.00)
Posted by trobbins on 2022-04-29, 14:23:27 (167.179.137.188)
It seems to fit a gassy valve developing, with grid voltage going more positive by its own grid current. If your amp can handle it then you could confirm by swapping the suspect tube and confirm the g .......
26: Tube DIY Asylum, RE: is it the famous (0.00)
Posted by trobbins on 2022-03-29, 17:07:17 (167.179.137.188)
It seems strange that Crowhurst didn't discuss adding a zobel network across the speaker output, as a way to retain a resistive load characteristic (ie. a work-around to the issue of inductive speaker .......
27: Tube DIY Asylum, RE: Thanks. it is in the signal path so I wish there was a way . . . (0.00)
Posted by trobbins on 2022-03-25, 21:30:03 (167.179.137.188)
Perhaps best to post/link a schematic so that we don't misinterpret what you are trying to do. .......
28: Tube DIY Asylum, RE: I have 600 volts going across a 2 watt resistor but . . (0.00)
Posted by trobbins on 2022-03-25, 21:11:39 (167.179.137.188)
Series connection is needed. Eg if R is final value needed then use two R/2 value resistors connected in series. .......
29: Tube DIY Asylum, RE: TV Damper Diode in Bridge - elevate heater or not? (0.00)
Posted by trobbins on 2022-03-23, 04:13:52 (167.179.137.188)
It doesn't. The hk rating comment was related to the latter part of the previous post. .......
30: Tube DIY Asylum, RE: TV Damper Diode in Bridge - elevate heater or not? (0.00)
Posted by trobbins on 2022-03-21, 23:00:53 (167.179.137.188)
Heater is below cathode for full-wave diodes, but is above cathode for the other two bridge diodes. 6CL3 has asymmetrical heater-cathode voltage capabilities. .......
31: Tube DIY Asylum, RE: How to use a bolt to improve hum spectrum (0.00)
Posted by trobbins on 2022-03-03, 23:06:52 (167.179.137.188)
Because the leakage inductance of your 150V secondary winding is likely to be a few mH, and possibly up to 10mH, which makes it about the same level as the 'bolt' inductor (which you were happy to inc .......
32: Tube DIY Asylum, RE: How to use a bolt to improve hum spectrum (0.00)
Posted by trobbins on 2022-03-03, 15:35:04 (167.179.137.188)
Where is the transformer leakage inductance model component in your simulation schematic? Did you measure that leakage inductance value in a real transformer? Did you measure the inductance of the 'bo .......
33: Tube DIY Asylum, RE: Putting diodes between the rectifier tube for protection?? (0.00)
Posted by trobbins on 2022-02-10, 15:56:03 (167.179.137.188)
Yes I was a bit terse. The hassle is that some get very limited information from responses on a thread to such a topic. This thread is such an example, as the OP has apparently decided not to add this .......
34: Tube DIY Asylum, RE: Putting diodes between the rectifier tube for protection?? (0.00)
Posted by trobbins on 2022-02-09, 15:19:05 (167.179.137.188)
Is that all the internet based insight you could find? There are a large number of hifi amp threads on various forums where that mod has been done - did you miss them? Reliability is more than just o .......
35: Tube DIY Asylum, RE: Putting diodes between the rectifier tube for protection?? (0.00)
Posted by trobbins on 2022-02-09, 13:54:10 (167.179.137.188)
Perhaps do some internet searching and collate what you find and post back. .......
36: Tube DIY Asylum, RE: No (0.00)
Posted by trobbins on 2022-02-01, 22:29:29 (167.179.137.188)
The 5AR4 does not introduce the imbalance being principally discussed in this thread. Indirectly heated rectifiers like the 5AR4 show imbalance due to differences in cathode emissions, and difference .......
37: Tube DIY Asylum, RE: Rectifier question (0.00)
Posted by trobbins on 2022-02-01, 22:18:57 (167.179.137.188)
It is good practise, and sometimes regulatory, not to add parts that can fail to the neutral side of a mains primary circuit. So imho it would be poor practise to add a resistor in the primary side ne .......
38: Tube DIY Asylum, RE: How far do you chase hum? (0.00)
Posted by trobbins on 2022-01-31, 18:31:31 (167.179.137.188)
Perhaps when you run out of instrumentation that is good enough to localise the various sources of that remnant hum, and the incentive to keep identifying. .......
39: Tube DIY Asylum, RE: So you're saying 2 resistors? (0.00)
Posted by trobbins on 2022-01-19, 14:25:20 (167.179.137.188)
That's up to you entirely and how your AZ11 performs. As discussed, there is a difference in voltage balance. Nowadays few transformers include the heater CT, so that aspect often doesn't even get a m .......
40: Tube DIY Asylum, RE: Rectifier question (0.00)
Posted by trobbins on 2022-01-19, 13:03:59 (167.179.137.188)
You could use just one resistor as indicated, although that upsets the balanced voltages wrt the output (whether that is significant depends also on the balance inherent in the AZ11 itself for the eff .......
41: Tube DIY Asylum, RE: IMD measurement (0.00)
Posted by trobbins on 2022-01-18, 01:43:30 (167.179.137.188)
Are you going to test each sample tube separately, or tube roll the tubes when the amp is up and running? Do you have a way of changing your circuit simulation triode model to make it compare well wit .......
42: Tube DIY Asylum, RE: Study of a low IMD all 6SN7 amplifier (0.00)
Posted by trobbins on 2022-01-17, 14:05:22 (167.179.137.188)
What are you going to use to measure IMD in your prototype amp? Have you set up an IMD test circuit to valve-swap and order the performance of the valves you have? I have only tested a batch of 6SN7 .......
43: Tube DIY Asylum, RE: I may have found to source of the hum (0.00)
Posted by trobbins on 2022-01-09, 18:27:07 (167.179.137.188)
You have also averted an electrically dangerous construction fault, as all metal parts within an amp should be electrically bonded to chassis (and hence to main protective earth). Seems to me like ano .......
44: Tube DIY Asylum, RE: This leads to another detail regarding hybrid supplies... (0.00)
Posted by trobbins on 2022-01-06, 20:13:33 (167.179.137.188)
Somewhat similar to balancing resistors, imho balancing caps are not needed for secondary side mains voltage rectification as the dV/dt across the diode won't get to a high enough level, and the other .......
45: Tube DIY Asylum, RE: High Voltage Resistors (0.00)
Posted by trobbins on 2022-01-06, 18:14:56 (167.179.137.188)
Note that a diode like a 1N4007 has a 1kV rating, but likely supports a PIV of about 1.5kV before leakage current increases significantly. If there is a transient mains over voltage, and there is no d .......
46: Tube DIY Asylum, RE: McIntosh 240 (0.00)
Posted by trobbins on 2022-01-02, 15:51:13 (167.179.137.188)
There have been a number of thread postings where the output and/or power transformer has failed, and the owner has had great difficulty in getting a replacement. If you do get one, then I highly sugg .......
47: Tube DIY Asylum, RE: Results so far (0.00)
Posted by trobbins on 2022-01-01, 18:32:52 (167.179.137.188)
If R5 is shorted then there should be no global feedback applied but an input signal should still pass through the amp and the output signal level should be significantly higher (compared to when feed .......
48: Tube DIY Asylum, RE: Results so far (0.00)
Posted by trobbins on 2022-01-01, 13:48:06 (167.179.137.188)
"Shorting R5 - hum almost gone, replaced with a static and no music through that channel with jumper" - what does no music through that channel mean? Are you saying that signal passes, but then not wh .......
49: Tube DIY Asylum, RE: Please help finding this darn hum (0.00)
Posted by trobbins on 2021-12-30, 17:04:54 (180.150.38.222)
Some testing steps to try: Lift one leg of C1 to localise fault options. Put a shorting link across R3. Put a 100uF across R9. .......
50: Tube DIY Asylum, RE: Alodine / Iridite Chromate Conversion (0.00)
Posted by trobbins on 2021-12-28, 21:17:27 (167.179.137.188)
For DIY, perhaps best to do a few small aluminium swatches and compare results. You could also try and contact a seller of power industrial semiconductors (eg. Fastron in Melb), as they sell large hea .......
51: Tube DIY Asylum, RE: Increase choke inductance will smooth out the treble harsh? (0.00)
Posted by trobbins on 2021-12-26, 09:09:04 (167.179.137.188)
What has that got to do with a frequency response plot? .......
52: Tube DIY Asylum, RE: Increase choke inductance will smooth out the treble harsh? (0.00)
Posted by trobbins on 2021-12-25, 14:38:08 (167.179.137.188)
Eric, I don't see any frequency response plots in this thread?? .......
53: Tube DIY Asylum, RE: Test point wiring best practices question (0.00)
Posted by trobbins on 2021-12-22, 14:36:06 (167.179.137.188)
Yeh, on my restored amps I use an octal (or DB9 or 5-pin) to externally monitor a 100:1 attenuated B+ and 2nd B+ as well as individual cathode sense currents (using 10R resistors) and a common cathode .......
54: Tube DIY Asylum, RE: Coupling capacitor with parallel RC - any reason ??? (0.00)
Posted by trobbins on 2021-12-11, 14:32:35 (167.179.137.188)
It is part of low-frequency stability management, as it provides a step (albeit small) in the low frequency roll-off of the forward path gain. The first two stages are dc coupled, so no CR network to .......
55: Tube DIY Asylum, RE: Additional details... (0.00)
Posted by trobbins on 2021-12-02, 16:55:45 (167.179.137.188)
No, I'm just saying that if there is no cathode cloud then applying a high grid voltage should reduce the number of molecules being hit, and the number of ions returning to the cathode with a high ene .......
56: Tube DIY Asylum, RE: Additional details... (0.00)
Posted by trobbins on 2021-12-02, 14:07:27 (167.179.137.188)
The nominal situations are whether there is a buffer electron cloud around the cathode (due to the cathode being sufficiently hot), or not. So any autobias timing should aim to account for cathode tem .......
57: Tube DIY Asylum, RE: Cathode Stripping (0.00)
Posted by trobbins on 2021-12-01, 18:59:53 (167.179.137.188)
I'd agree with all that although the 845 and 211 tubes have very high grid voltage capabilities, and the 211 is even specced at 400V, so using -250V seems well within reason although any actual value .......
58: Tube DIY Asylum, RE: Losses in Output Transformers (0.00)
Posted by trobbins on 2021-09-15, 18:24:46 (167.179.137.188)
Are you using regulated B+ and screen supplies, with no stopper resistors, and accounting for winding dc voltage drop, and swapped in a few new valves to see if their was any variation? .......
59: Tube DIY Asylum, RE: LMAO.... (0.00)
Posted by trobbins on 2021-08-27, 06:52:41 (167.179.137.188)
What are you talking about? .......
60: Tube DIY Asylum, RE: Grid Protection w/ Current Limiting Diode (0.00)
Posted by trobbins on 2021-08-26, 22:31:55 (167.179.137.188)
Figure 1.2 in link: .......
61: Tube DIY Asylum, RE: Grid Protection w/ Current Limiting Diode (0.00)
Posted by trobbins on 2021-08-26, 20:53:04 (167.179.137.188)
Can just use a power diode in place of the neon - Merlin discusses that at ValveWizard. NE-2 may age if it included some radioactive gas so need to check it does actually work as intended. Once the NE .......
62: Tube DIY Asylum, RE: What I've done probably does not per se rule out external leakage or arcing (0.00)
Posted by trobbins on 2021-08-04, 21:35:28 (167.179.137.188)
If you can then calculate the working voltages across any insulation barrier within a transformer, then that guides the test voltage to use for IR measurement. Eg +1kVpk on one winding, and -2kVpk on .......
63: Tube DIY Asylum, RE: What I've done probably does not per se rule out external leakage or arcing (0.00)
Posted by trobbins on 2021-08-04, 21:14:05 (167.179.137.188)
Insulation resistance measurement is a basic test for leakage or breakdown/arcing within a transformer, as it generates a certain DCV (or ACV) across an insulation barrier (eg. secondary to core, or a .......
64: Tube DIY Asylum, RE: Recommendations for repair of a power transformer (0.00)
Posted by trobbins on 2021-08-04, 19:30:32 (167.179.137.188)
Have you confirmed it is the transformer, and not an external leakage/arcing problem? If you have the transformer specs, and access to an insulation resistance meter (such as a Megger) with say 5kV te .......
65: Tube DIY Asylum, RE: Dynaco C354 Choke Measured Value (0.00)
Posted by trobbins on 2021-07-16, 22:13:29 (167.179.137.188)
Note that the choke inductance will vary with excitation voltage, and the ST70 application has about 28Vpp across the choke at idle, and likely a lot more at high audio power (based on simple PSU2 sim .......
66: Tubes Asylum, RE: Vale Patrick Turner (0.00)
Posted by trobbins on 2021-05-23, 21:23:01 (167.179.137.188)
That is exceedingly sad to hear - as I have emailed him a few times a year for the last 5 years, but no response since January. Patrick certainly didn't hold back with his views - which was part of hi .......
67: Tube DIY Asylum, RE: ARTA measurement system for 2021 ? (0.00)
Posted by trobbins on 2021-05-04, 16:39:37 (167.179.137.188)
I guess there are always going to be some quirky installations due to different security permissions. Yes the latest beta version is what I have used on a few Win10 PC's/laptops. I vaguely recall that .......
68: Tube DIY Asylum, RE: ARTA measurement system for 2021 ? (0.00)
Posted by trobbins on 2021-05-04, 06:21:03 (167.179.137.188)
My 0404 USB works with Win10. Did you have the card version? .......
69: Tube DIY Asylum, RE: ARTA measurement system for 2021 ? (0.00)
Posted by trobbins on 2021-05-04, 06:18:14 (167.179.137.188)
Are you saying the fault is the input jack? Can you bypass that? .......
70: Tube DIY Asylum, RE: Diode Tweak (0.00)
Posted by trobbins on 2021-04-28, 19:45:49 (167.179.137.188)
Eli, there really isn't any switching transient in a vintage valve diode application, due to the relatively high winding resistance and self-capacitance, and the lowish diode peak current pulse (dicta .......
71: Tube DIY Asylum, RE: Diode Tweak (0.00)
Posted by trobbins on 2021-04-28, 16:21:36 (167.179.137.188)
A valve diode typically has way lower ratings for peak current than a 1N4007. Unless the person who suggested a higher current rated diode is referring to a significantly different application, then e .......
72: Tube DIY Asylum, RE: ss diode on gz34 (0.00)
Posted by trobbins on 2021-04-27, 17:08:50 (167.179.137.188)
As indicated in other posts, some amps can stress the rectifier tube sufficiently for anecdotal failure numbers and short life to become noticeable. There is also non-zero failure rate in other amps j .......
73: Tube DIY Asylum, RE: ss diode on gz34 (0.00)
Posted by trobbins on 2021-04-27, 05:40:28 (167.179.137.188)
Detrimental impact ? .......
74: Tube DIY Asylum, RE: Bakelite Sockets (0.00)
Posted by trobbins on 2021-04-17, 18:18:46 (167.179.137.188)
Some applications require the lowest possible leakage resistance between pins, but I doubt you are venturing in to that domain. If using for output stage valves, then orientation of the sockets to all .......
75: Tube DIY Asylum, RE: Transformer Interaction - Fact or Fiction? (0.00)
Posted by trobbins on 2021-04-06, 18:17:04 (167.179.137.188)
Thanks for that :-). I can now see that the results are from John's one electron website. So PP stage is operating in pentode mode, except for those UL listings. The comments about testing with feedba .......
76: Tube DIY Asylum, RE: Transformer Interaction - Fact or Fiction? (0.00)
Posted by trobbins on 2021-04-06, 15:50:39 (167.179.137.188)
Is the John Atwood list related to a particular test jig or amplifier (as the notes seem to indicate)? .......
77: Tube DIY Asylum, RE: Transformer Interaction - Fact or Fiction? (0.00)
Posted by trobbins on 2021-04-02, 14:46:50 (167.179.137.188)
It seems that you have covered your own concerns if you can find hum levels on the SCA-35. Note that all because a signal in one winding can be picked up by another winding in another transformer, tha .......
78: Tube DIY Asylum, RE: 5u4 choke input question (0.00)
Posted by trobbins on 2021-04-02, 00:17:35 (167.179.137.188)
I'd suggest using PSUD2 to confirm correct operation (choke current always above zero) for the required output voltage and current range when all the circuit parameters are included (effective transfo .......
79: Tube DIY Asylum, RE: Thanks - I wonder why this doesn't short? (0.00)
Posted by trobbins on 2021-04-01, 20:48:45 (167.179.137.188)
I think it might come back to grid conduction damage, as any arc would be current limited by the B+ and circuit resistances. .......
80: Tube DIY Asylum, RE: Cathodyne Protection (0.00)
Posted by trobbins on 2021-04-01, 02:49:40 (167.179.137.188)
12B4 has a 200V heater-cathode limit, so that may be a concern for starters. The peak negative grid voltage rating is 250V, and although you aren't taking the grid negative at startup, it will have a .......
81: Tube DIY Asylum, RE: Another Transformer Topic (0.00)
Posted by trobbins on 2021-03-28, 01:23:03 (167.179.137.188)
I have a bit of a problem with Fig. 1.4 in that Morgan Jones book clip. Leakage flux predominantly loops from the coils on either side of the core, whereas that diagram portrays them looping through t .......
82: Tube DIY Asylum, RE: Another Transformer Topic (0.00)
Posted by trobbins on 2021-03-27, 18:06:24 (167.179.137.188)
Yeh it is quite a complex situation to try and rationalise what level of signal can be transferred into another winding. One aspect is that a simple test setup only passes magnetising current through .......
83: Tube DIY Asylum, RE: That's the same fomuula I use ... (0.00)
Posted by trobbins on 2021-03-25, 15:20:52 (167.179.137.188)
As an aside, core heating and core temperature feature strongly in smps design with ferrite cores, as ferrite core loss becomes a significant total loss contributor, and thermal management of the core .......
84: Tube DIY Asylum, RE: Question about power transformer rating with LC choke and others (0.00)
Posted by trobbins on 2021-02-25, 17:05:52 (167.179.137.188)
The Lundahl LL1685 does identify that it is capable of being used for choke input application, and provides a 330Vrms 100Hz max rating. I'd strongly suggest the OP starts to use PSUD2 to work through .......
85: Tube DIY Asylum, RE: Yep, so did Hammond tonewheel organs (0.00)
Posted by trobbins on 2021-02-21, 14:35:07 (167.179.137.188)
My view is that using grid stopper and grid leak to identify specific resistors on a schematic (or in an amp if looking at a photo) removes ambiguity about what may be being referred to. I'd suggest t .......
86: Tube DIY Asylum, RE: Yep, so did Hammond tonewheel organs (0.00)
Posted by trobbins on 2021-02-21, 13:55:24 (167.179.137.188)
I would happily continue to use grid leak and grid stopper to identify the two commonly seen resistors attached to a signal input grid G1. To me just the term grid resistor is ambiguous for forum disc .......
87: Tube DIY Asylum, RE: Power supply problem (0.00)
Posted by trobbins on 2021-02-03, 23:59:19 (167.179.137.188)
"After disconnecting the tranny I discovered that by switching the center tap wires, I get normal output from the transformer. The problem is that the center tap for the 6.3 and the tap for the main s .......
88: Tube DIY Asylum, RE: Power supply problem (0.00)
Posted by trobbins on 2021-02-03, 18:42:49 (167.179.137.188)
Heater is often best indicator of local mains voltage compared to what the transformer primary was designed for. +10% unloaded heater voltage would be nominal, and you measure +16%, so it is likely th .......
89: Tube DIY Asylum, RE: Power supply problem (0.00)
Posted by trobbins on 2021-02-03, 16:40:52 (167.179.137.188)
Schematic? Have you measured your mains voltage and compared that to schematic or to equipment data/manual for nominal voltage that the equipment was made for? What voltage is the 6.3V heater at ? You .......
90: Tube DIY Asylum, RE: Bad transformer? Never seen this before. (0.00)
Posted by trobbins on 2021-01-27, 22:18:37 (167.179.137.188)
Check the winding resistances with a meter (primary side, and each secondary HT half). If they are nominal, then pull the 5AR4 out and measure the secondary side 250-0 and 0-250Vrms nominal levels. Al .......
91: Tube DIY Asylum, RE: Decoupling questions (0.00)
Posted by trobbins on 2021-01-22, 17:04:32 (167.179.137.188)
Crohurst audio book relevant chapters .......
92: Tube DIY Asylum, RE: Decoupling questions (0.00)
Posted by trobbins on 2021-01-22, 17:01:25 (167.179.137.188)
Another reference in power distribution section .......
93: Tube DIY Asylum, RE: Decoupling questions (0.00)
Posted by trobbins on 2021-01-22, 16:59:51 (167.179.137.188)
It appears that the topic is power supply decoupling to individual gain stages within an amp. Yes references specifically to that topic of power distribution are not typically covered in books or arti .......
94: Tube DIY Asylum, RE: Q About Elevated Heaters (0.00)
Posted by trobbins on 2021-01-17, 23:20:23 (167.179.137.188)
My take on what are the known causes of hum, including as much detail as I can muster, is in the link below. It is a wee bit technical sometimes. .......
95: Tube DIY Asylum, RE: Q About Elevated Heaters (0.00)
Posted by trobbins on 2021-01-17, 20:10:33 (167.179.137.188)
The DC elevation, apart from easing the voltage stress on the heater cathode interface (as there are datasheet limits), also has a 'general' benefit of increasing the leakage resistance between heater .......
96: Tube DIY Asylum, RE: Q About Elevated Heaters (0.00)
Posted by trobbins on 2021-01-17, 19:15:15 (167.179.137.188)
The humdinger normally balances any capacitive leakage current getting to the valve grid by connecting a mid-point voltage to gnd. In any amp, the wiring and layout of parts may allow one side of the .......
97: Tube DIY Asylum, RE: That is not a problem... (0.00)
Posted by trobbins on 2021-01-14, 14:25:03 (167.179.137.188)
SiC diodes are different beasts than a pn power diode - they need careful scrutiny of the available datasheet. As an example, the TO-220 package of the Cree C4D02120A is designed for heatsinking. If t .......
98: Tube DIY Asylum, RE: That is not a problem... (0.00)
Posted by trobbins on 2021-01-13, 15:52:47 (167.179.137.188)
FWIW, I just did a comparison assessment of the Cree C4D02120A when that part is just used 'free-standing' (ie. without heatsinking). Its current capability appears to be similar to a 1N4007 for a cho .......
99: Tube DIY Asylum, RE: Why no snubbers ? (0.00)
Posted by trobbins on 2021-01-13, 14:24:27 (167.179.137.188)
If planning to use a SiC then my advise is to call and ask the question as to whether a particular SiC diode can manage a particular mains rectifier application for current rating, as the peak current .......
100: Tube DIY Asylum, RE: Why no snubbers ? (0.00)
Posted by trobbins on 2021-01-13, 04:57:37 (167.179.137.188)
The reference was to section 2 of the link, which is 3 pages long. The comment about batch relates to any diode from the same batch, not to sort diodes from within a batch. Most of us buy a 'batch' of .......
101: Tube DIY Asylum, RE: OK to series connect 2 1000v/1A diode rectifiers instead of 1 1.2kv (0.00)
Posted by trobbins on 2021-01-12, 15:45:51 (167.179.137.188)
Thanks, that indicates a 360-400Vdc B+, so connecting 2x UF4007 in series for each of the full-wave rectifier 'diodes' is appropriate and provides sufficient PIV margin for a 300-0-300V secondary wind .......
102: Tube DIY Asylum, RE: OK to series connect 2 1000v/1A diode rectifiers instead of 1 1.2kv (0.00)
Posted by trobbins on 2021-01-12, 14:43:10 (167.179.137.188)
I would recommend not using snubbers across diodes such as suggested. Soldering two UF4007 in series so they have the same die temperature, and using UF4007 from the same batch, should be sufficient f .......
103: Tube DIY Asylum, RE: found this interesting (0.00)
Posted by trobbins on 2021-01-10, 20:30:28 (167.179.137.188)
A slight tweak of wording: The commutation of the diodes shock-excites the RLC of the leakage L in each half of the power trans secondary, and any stray C through the choke and the transformer seconda .......
104: Tube DIY Asylum, RE: found this interesting (0.00)
Posted by trobbins on 2021-01-10, 18:47:00 (167.179.137.188)
Are you snubbing the diode-choke node in your amp power supplies to manage the large and violent dI/dt during commutation? .......
105: Tube DIY Asylum, RE: found this interesting (0.00)
Posted by trobbins on 2021-01-10, 14:20:23 (167.179.137.188)
Doh - this post should be located further 'down' in this thread. Capacitor input power supplies have always had those peaky rectifier currents, for well over 70 years. Are you saying that pretty much .......
106: Tube DIY Asylum, RE: found this interesting (0.00)
Posted by trobbins on 2021-01-10, 04:48:45 (167.179.137.188)
Most people just aim to comply with the max capacitance requirement, and many datasheets use a max capacitance spec that ensures the continuous peak and the surge peak spec levels are not exceeded for .......
107: Tubes Asylum, RE: Anyone used an induction heater to re-activate the getter? (0.00)
Posted by trobbins on 2020-12-29, 23:37:21 (167.179.137.188)
Pictureguy, strangely I do have a pretty good understanding of valve getter operation, and sadly you have not done your homework on valve getter operation. There are some excellent technical reference .......
108: Tubes Asylum, RE: Tube/Valve Lifespan (0.00)
Posted by trobbins on 2020-12-29, 23:19:43 (167.179.137.188)
I find it strange that some spend big-bucks on an amp, only to operate it without any form of maintenance until it sounds suspect. I guess the example is a pricey vintage car - drive it till you hear .......
109: Tubes Asylum, RE: Anyone used an induction heater to re-activate the getter? (0.00)
Posted by trobbins on 2020-12-29, 22:57:54 (167.179.137.188)
I think the realizable aim is to heat the getter flash on the inner glass surface, such that some percentage of the getter flash becomes active. For a vintage tube, the getter flash may well have bec .......
110: Tube DIY Asylum, RE: RCA Application Note (0.00)
Posted by trobbins on 2020-12-09, 14:41:37 (167.179.137.188)
The heater-cathode leakage was initially detailed as a variation in resistance, by Klemperer in 1936, and that way of viewing it (compared to a hum level measurement) continued in later decades. I hav .......
111: Tube DIY Asylum, RE: Voltage margin on PS caps and unusual cathode resistors. (0.00)
Posted by trobbins on 2020-10-01, 19:31:18 (167.179.137.188)
Standby B+ voltage is with the output stage tubes heated and loading down the amplifier. Given the amp uses ss diodes, there is 10-12 seconds when a higher DCV is applied to all caps in the amp. At po .......
112: Tube DIY Asylum, RE: Voltage regulator tubes (0.00)
Posted by trobbins on 2020-09-03, 23:29:19 (167.179.137.188)
I'm not certain if the radioactive elements were aimed at just better regulation or if they had any 'striking voltage' influence. It will be the peak voltage seen by the OA2 before striking that is th .......
113: Tube DIY Asylum, RE: Voltage regulator tubes (0.00)
Posted by trobbins on 2020-09-03, 22:39:37 (167.179.137.188)
Different tube chemistries may have different strike levels - that was why I raised the option of testing to a higher initial B+ level. The final plate voltage may be similar if the 'operating' OA2 is .......
114: Tube DIY Asylum, RE: Voltage regulator tubes (0.00)
Posted by trobbins on 2020-09-03, 22:12:13 (167.179.137.188)
The circuit may not provide sufficient initial over-voltage for the regulator tube to 'strike', in which case the tubes may not be 'bad'. One other possibility is that those regulator tubes may includ .......
115: 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 trobbins on 2020-08-31, 19:52:49 (167.179.137.188)
It can get a bit technical and there is a link below to a design article. If you can measure the new PT winding resistances, and confirm the operating voltages and currents and circuitry (I can see a .......
116: 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 trobbins on 2020-08-31, 19:26:56 (167.179.137.188)
I would recommend fitting at least a 1N4007 in series with each 5U4 anode, and preferably a CT fuse, as the best means to avoid collatoral PT damage in to the future. .......
117: 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 trobbins on 2020-08-31, 17:53:54 (167.179.137.188)
You say after many posts that the transformer is 'shot'. Prior to that you indicate a fuse blew and the transformer was hot and smelt. How have you confirmed/tested that the transformer is 'shot'? ::: .......
118: Tube DIY Asylum, RE: While everyone has the troubleshooting hat on... (0.00)
Posted by trobbins on 2020-08-31, 17:46:08 (167.179.137.188)
Buy some electronics contact cleaner spray with micro-nozal and remove/insert and spray all valve pins and any other plugs/sockets, battery connections, and pots if you can access them. If you have a .......
119: Tube DIY Asylum, RE: What has heater/cathode (voltage) rating got to do with this topic? (0.00)
Posted by trobbins on 2020-08-08, 18:38:04 (167.179.137.188)
Just clarifying that turning on an amplifier, where each tube experiences a normal heater surge current whilst the heater/filament is heating up, is not in any way violating a tube rating. I've been l .......
120: Tube DIY Asylum, RE: Uhhhh Really? (0.00)
Posted by trobbins on 2020-08-06, 19:35:42 (167.179.137.188)
You made the comment 'most tubes fail from the heater/filament'. I'd suggest that is your view, but not backed by any rigorous statistics or testing or other reviewed form of assessment. You may have .......
121: Tube DIY Asylum, RE: Tube Life in Triode or Tetrode (0.00)
Posted by trobbins on 2020-08-06, 15:55:08 (167.179.137.188)
Two comments are not supported by statistical evidence - 'most tubes fail from the heater/filament' 'having a harsh turn-on surge' Those comments are just isolated heresay. That's not to say that an .......
122: Tube DIY Asylum, RE: When strapping an output pentode to triode.... (0.00)
Posted by trobbins on 2020-08-05, 22:16:52 (167.179.137.188)
In practice, the open-loop gain will depend on the output stage configuration. The voltage gain from valve grid to anode is simplistically the mu multiplied by the anode resistance (ra), and although .......
123: Tube DIY Asylum, RE: When strapping an output pentode to triode.... (0.00)
Posted by trobbins on 2020-08-05, 00:02:34 (167.179.137.188)
Sure does change the open loop gain, so if you are after a specific feedback dB level, then you may need to adjust the feedback network, depending on how large the open loop gain is. Pentode mode has .......
124: Vintage Asylum, RE: "Magic Eye Tube Vu Meters": Do such devices exist or be made? (0.00)
Posted by trobbins on 2020-07-27, 17:30:43 (167.179.137.188)
Typical VU meters use a dB scale - similar to how a volume pot is not linear, but is logarithmic in how its rotation changes its resistance. However a typical magic eye valve varies its display over a .......
125: Tube DIY Asylum, RE: Williamson revisited (0.00)
Posted by trobbins on 2020-06-07, 18:57:08 (167.179.137.188)
I'd recommend you confirm the feedback level as no more 20dB (by measurement of signal output voltage difference when feedback is connected and disconnected, and with a low level output). I'd also rec .......
126: Tube DIY Asylum, RE: Got it working (0.00)
Posted by trobbins on 2020-05-11, 22:13:03 (167.179.137.188)
Sounds like you are through the first phase, with a working amp. Minimising hum can be a fickle process - there are some faultfinding guidelines in link that may help if you haven't been down that pat .......
127: Tube DIY Asylum, RE: Still am concerned (0.00)
Posted by trobbins on 2020-05-09, 19:31:02 (167.179.137.188)
Regulated screen voltage can be one means to minimising distortion, and datasheets will present regulated rail data to show what distotion can be achieved. In PA and guitar land, screens are almost ne .......
128: Tube DIY Asylum, RE: Refurbing old PA amp, need help with PSU (0.00)
Posted by trobbins on 2020-05-08, 15:40:45 (167.179.137.188)
A lot of vintage amps had internal rail loads - mainly to sustain choke current to above nominal critical conduction level, which provides a better regulation range, and reduces stress on the filter c .......
129: Tube DIY Asylum, RE: Refurbing old PA amp, need help with PSU (0.00)
Posted by trobbins on 2020-05-07, 21:03:46 (167.179.137.188)
Restoring old PA amps can be fun, but also tedious if all the wire insulation is poor, and many resistors have drifted too much, and any electrolytic needs replacing. It would be a rarity if the amp h .......
130: Vintage Asylum, RE: Who restores vintage NAD 3020 series amps (0.00)
Posted by trobbins on 2020-05-07, 20:50:38 (167.179.137.188)
I repaired and restored a failed unit recently. There are a few revisions of pcb and layout and circuitry. I did a recap, and added output stage transistor base and emitter resistors for enhanced prot .......
131: Tube DIY Asylum, RE: battery in series with the grid (0.00)
Posted by trobbins on 2020-04-18, 00:03:34 (167.179.137.188)
Battery bias was used in the 'early' days (eg. 1930's), as a way to alleviate hum and allow a cathode to be directly grounded (grid-leak bias has its issues). .......
132: Tube DIY Asylum, RE: ITC inductance question (0.00)
Posted by trobbins on 2020-02-19, 22:03:40 (110.145.182.146)
You can also measure winding inductance with DC using a relatively simple technique - see link. That can clarify your design equation path, as well as identify the inductance variation on either side .......
133: Tubes Asylum, RE: Damn, just burned out a filament (0.00)
Posted by trobbins on 2020-02-17, 17:50:37 (110.145.182.146)
I would caution adding any tubes until a clean bill of health for the existing amp, as the fault cause is unknown. Without knowing details, I would be using a variac and ss diodes (in place of the 5AR .......
134: Tubes Asylum, RE: They DO look kinda Russian... (0.00)
Posted by trobbins on 2020-02-06, 01:20:54 (167.179.137.188)
I have five 807's with that shape of top mica spacer, but none of about 20 various 807's have that shape of base shield below the lower mica disk, or that shape of getter cup. The two Brimar's I have .......
135: Tube DIY Asylum, RE: Reduce 3rd order distortion, CCS or carhode Degeneration? (0.00)
Posted by trobbins on 2020-01-30, 01:17:48 (167.179.137.188)
Are you doing all assessments by ear, and perhaps a scope (although that will only show gross distortion)? If so then it would seem a bit suspect if you were then not making the effort to acquire any .......
136: Vintage Asylum, RE: Testing a Heathkit W6M Amp (0.00)
Posted by trobbins on 2019-12-28, 16:57:45 (167.179.137.188)
Have you been able to check the various resistances yet. Even if they are as expected, it can be well worthwhile doing a few more tests before committing to a lot of effort restoring, as sometimes a p .......
137: Tube DIY Asylum, RE: feedback ratio or replicating a FB amount (0.00)
Posted by trobbins on 2019-11-25, 16:12:31 (167.179.137.188)
Morgan Jones V3 copy was on the web at one time - perhaps still is. Yeh I missed the self bias/feedback only aspect - sorry. There are a few theory books on-line that I would have thought went through .......
138: Tube DIY Asylum, RE: feedback ratio or replicating a FB amount (0.00)
Posted by trobbins on 2019-11-25, 00:29:33 (167.179.137.188)
Morgan Jones V3 goes through a design example for combined voltage and current feedback - its more complex than just voltage, or current feedback alone. There is also an example in section 2 of link o .......
139: Tube DIY Asylum, RE: You read my mind (0.00)
Posted by trobbins on 2019-11-15, 15:25:30 (167.179.137.188)
Building a clone amp for hi-fi and getting it to 'work' can be the full story for many. As well, it can be worth making the effort to confirm that the amp is performing properly over frequency, power .......
140: Tube DIY Asylum, RE: What to do with this HiWatt monstrosity? (0.00)
Posted by trobbins on 2019-11-14, 21:16:45 (110.145.182.146)
If you still have lower power rating amps waiting for refurb, then I'd suggest doing them first and putting that chassis to the side for the moment. Nothing beats exposure and experience when it comes .......
141: Tube DIY Asylum, RE: 45 amp cathode resistor explanation please. (0.00)
Posted by trobbins on 2019-11-14, 20:30:36 (110.145.182.146)
In addition, this is a low wattage output amp, so the output transformer primary will drop significant voltage (perhaps circa 20V for 1W idle dissipation for a 3W rated transformer), and the power sup .......
142: Tube DIY Asylum, RE: what kind of tranny is this? (0.00)
Posted by trobbins on 2019-11-03, 13:59:30 (167.179.137.188)
To appropriately use it you would need to measure some of its parameters. The simplest parameter to determine is primary impedance. Measure the turns ratios of P-B, 600 and 8 ohm windings. Look up som .......
143: Tube DIY Asylum, RE: FaWhoop! (0.00)
Posted by trobbins on 2019-10-22, 19:52:10 (110.145.182.146)
Most would think of hum as an unwanted signal, tainting the amplified sound being listened to. However, one investigation by a German Uni (Project Wildcat) used a Fender Bassman 5F6-A to compare defau .......
144: Tubes Asylum, RE: 5R4 / 5R4GY Tube Rectifiers - A Mini Shoot-out (0.00)
Posted by trobbins on 2019-10-20, 18:09:06 (110.145.182.146)
Even within a brand, each valve out of a batch will show variation in the on-resistance of each diode in the valve, and variation in when that on-resistance starts to change at the peak of the current .......
145: Tubes Asylum, RE: Disastrous tube rolling (0.00)
Posted by trobbins on 2019-10-16, 18:49:21 (110.145.182.146)
"what if it happens again" is a good question that probably requires the cause to be confirmed, which in itself would require you to modify your speaker setup to avoid damage if testing. As Jim points .......
146: Tube DIY Asylum, RE: "Singing" Power Transformer (0.00)
Posted by trobbins on 2019-10-14, 22:17:39 (110.145.182.146)
610V is a little more than I would have thought, but yes in to the risky side of a 500V limit. I'd be inclined to tie the 6CA4 heater to its cathode, but you have two 6CA4 for separate supplies and wa .......
147: Tube DIY Asylum, RE: "Singing" Power Transformer (0.00)
Posted by trobbins on 2019-10-14, 16:28:16 (110.145.182.146)
The cathode voltage will follow the conducting anode voltage, minus the Vak conduction drop. The Hammond 710 has a 375-0-375V rating, with an anode peak of circa 530V, which could go higher depending .......
148: Tube DIY Asylum, RE: Room & spkr DSP Eq along with careful positioning can pretty well nail that. (0.00)
Posted by trobbins on 2019-10-14, 00:25:13 (167.179.137.188)
What I thought was interesting is that the live performance wasn't listened to. Granted it would be difficult to do a blind compare with enough statistical rigour, but the outcome could have been that .......
149: Tube DIY Asylum, RE: "Singing" Power Transformer (0.00)
Posted by trobbins on 2019-10-13, 18:18:57 (110.145.182.146)
The 6CA4 heater-cathode voltage rating is being exceeded in your design. Is that what you intended? .......
150: Tube DIY Asylum, RE: "Singing" Power Transformer (0.00)
Posted by trobbins on 2019-10-13, 03:18:25 (167.179.137.188)
Why is the heater grounded? It seems that using two heater transformers would have been a better design choice. Not sure if it is related to the singing, but there are likely to be circulating current .......
151: Tube DIY Asylum, RE: PS chokes (0.00)
Posted by trobbins on 2019-09-01, 04:06:14 (167.179.137.188)
Umm, choke input filter can have much better regulation than capacitor input over circa 10% to 100% loading range for a vintage valve diode rectifier and sufficient inductance. Some valve diode datash .......
152: Tubes Asylum, RE: Troubleshooting a possible rectifier tube problem (0.00)
Posted by trobbins on 2019-08-05, 15:31:40 (49.178.25.101)
You can add a 1N4007 in series with each diode anode. That should stop any rectifier arcing, so if you still see your light bulb brightening, then it is likely from cap breakdown. Adding ss diodes is .......
153: Tube DIY Asylum, RE: g2 regulation with zeners : schematic (0.00)
Posted by trobbins on 2019-07-07, 23:13:39 (167.179.137.188)
You may need to be cautious with how much power dissipation you run each zener at. 5W is typically a max junction temp with a good level of heatsinking. You may not achieve that heatsinking, and max o .......
154: Tube DIY Asylum, RE: I think the key words here are "a titch". (0.00)
Posted by trobbins on 2019-07-06, 18:03:16 (167.179.137.188)
Well Hafler was nulling out residual levels of distortion, and by 1958 had quite a bit of experience up his sleeve. He was apparently more a sales person than engineer, and could see the sales benefi .......
155: Tube DIY Asylum, RE: I'd love to know more about the claim (0.00)
Posted by trobbins on 2019-07-06, 03:15:29 (167.179.137.188)
I don't have a problem with Hafler's description of using a titch of common degeneration resistance to lower IM. I recall that Gingertube in his Baby Huey amp had identified that a mix of cathode bia .......
156: Tube DIY Asylum, RE: SE DC 6V6/6AQ5 : feedback & distortion study w/schematic. (0.00)
Posted by trobbins on 2019-03-31, 20:54:31 (110.145.182.146)
Are you saying that 60Hz hum was 80dB below 1W output fundamental test signal level ? If so, then how far below the 60Hz peak was your noise floor? (just enquiring to appreciate the test setup and how .......
157: Tube DIY Asylum, RE: SE DC 6V6/6AQ5 : feedback & distortion study w/schematic. (0.00)
Posted by trobbins on 2019-03-31, 18:00:45 (110.145.182.146)
Umm, there doesn't appear to be a grid leak for the 6V6 ? .......
158: Tube DIY Asylum, RE: SE DC 6V6/6AQ5 : feedback & distortion study w/schematic. (0.00)
Posted by trobbins on 2019-03-31, 17:58:24 (110.145.182.146)
Is your mains at 50 or 60Hz? Does ARTA isolate just the harmonics of test frequency, or also noise (eg. from hum)? How far below the dominant harmonics is your noise floor? Have you tube rolled to get .......
159: Tube DIY Asylum, RE: measured inductance vs. current thru a fixed filter choke (0.00)
Posted by trobbins on 2019-02-19, 15:41:58 (110.145.182.146)
For a typical CLC style filter choke, the inductance would increase from the rated inductance, perhaps by 10-20%, assuming it had the same AC voltage across it. There is likely to be no disadvantage t .......
160: Tubes Asylum, RE: Optimal EL84 operating point for UL pentode mode (0.00)
Posted by trobbins on 2019-02-10, 16:51:14 (110.145.182.146)
Just a query about how you would end up knowing you had an optimal operating setup - from the idle voltage and current levels - from the character of sound of the amp (assuming you were in to swapping .......
161: Tube DIY Asylum, RE: I removed it (0.00)
Posted by trobbins on 2019-01-30, 14:08:37 (1.127.111.232)
TN-S is the scheme used to distribute mains voltage and relates to how neutral and protective earth wiring is achieved. Google does a good explanation. Not all posters are from the same country, and s .......
162: Tube DIY Asylum, RE: Putting a CL or 2 on the high voltage secondary? (0.00)
Posted by trobbins on 2019-01-30, 01:59:59 (49.196.15.241)
I'd recommend no part is inserted in the neutral side of the mains ac circuit, if you have a TN-S mains. That would be poor diy practise, especially with an NTC part. .......
163: Tube DIY Asylum, RE: Alodine (0.00)
Posted by trobbins on 2019-01-06, 03:30:05 (167.179.137.188)
As I know it, alodining is a common option applied to new extruded aluminium heatsinks, including regions with a milled flat surface, as a client requires it. In general, alodining provides a long ser .......
164: Tubes Asylum, RE: Pilot 240 rectifier question (0.00)
Posted by trobbins on 2018-12-25, 15:46:08 (167.179.137.188)
Customer has the ability to check reviews, ask for references, build up a service history, post on forums - it's not all one-sided. Buying and operating vintage equipment is certainly caveat emptor st .......
165: Tubes Asylum, RE: Pilot 240 rectifier question (0.00)
Posted by trobbins on 2018-12-25, 14:59:32 (167.179.137.188)
The 5AR4 vintage datasheet provides peak current limit levels for both continuous operation and initial hot turn-on transient. If you can measure the power transformer primary winding resistance, and .......
166: Tube DIY Asylum, RE: Website (0.00)
Posted by trobbins on 2018-12-22, 15:18:17 (167.179.137.188)
It's a great hobby - just aiming to assist and collate where I can, as I appreciate there is a lot of information out there. .......
167: Tube DIY Asylum, RE: Type CL thermistors (0.00)
Posted by trobbins on 2018-12-22, 03:33:41 (167.179.137.188)
Eli, the time constant referenced in NTC datasheets is the cool-down time-constant, not the heat-up time constant - I think some have got the wrong idea of what time scale NTC in-rush suppression work .......
168: Tube DIY Asylum, RE: Maximum anode current in triode-connected pentode (0.00)
Posted by trobbins on 2018-12-19, 00:59:25 (167.179.137.188)
Tubes typically have a screen voltage limit when operating triode mode - I'd expect that is not much more than the tubes class AB screen voltage rating with fixed screen voltage. 807's had a 350V rat .......
169: Tube DIY Asylum, RE: The thought process :) (0.00)
Posted by trobbins on 2018-12-10, 14:40:48 (167.179.137.188)
Whether a heater is biased positive or negative, with respect to cathode, I'd suggest that unless you are knowingly operating the heater at a higher than specified voltage, then you should statistical .......
170: Tube DIY Asylum, RE: Thanks to everyone for comments, I've made a decision (0.00)
Posted by trobbins on 2018-12-10, 03:26:10 (167.179.137.188)
How did you decide that the output valves are not allowed to have their cathodes more negative than the heaters??? .......
171: Tube DIY Asylum, RE: Would you believe the ST70 does indeed have DC biased filaments?.... (0.00)
Posted by trobbins on 2018-11-24, 16:52:01 (119.17.139.167)
Yes the heater supply would have a high resistance connection to ground (through the paralleled heater-cathode resistances of all valves), and so the heater would not be truly floating. The heater CT .......
172: Tube DIY Asylum, RE: I think this is the bottom line... (0.00)
Posted by trobbins on 2018-11-21, 11:30:54 (1.144.107.124)
The equivalent circuit in Fig 8 of that article indicates that if the elevated dc voltage wasn't decoupled, then it would effectively insert a series noise voltage in to the loop (the 'noise' being an .......
173: Tube DIY Asylum, RE: Heater Elevation (0.00)
Posted by trobbins on 2018-11-21, 11:24:31 (1.144.107.124)
Some info in link may help appreciate what is happening: .......
174: Tube DIY Asylum, RE: Heater Elevation (0.00)
Posted by trobbins on 2018-11-21, 00:23:12 (1.144.107.131)
Some info in link may help appreciate what is happening: .......
175: Tube DIY Asylum, RE: PS explanation please (0.00)
Posted by trobbins on 2018-10-18, 15:34:26 (119.17.152.52)
One of the ECC83 triodes has cathode operating at 137V, which is too high if the heater is grounded. The elevated supply will be about 446*47/247 = 85V, which is about half-way between 27V and 137V. .......
176: Tube DIY Asylum, RE: stacked choke input high voltage power supply Can it be done? (0.00)
Posted by trobbins on 2018-09-24, 20:01:43 (110.145.182.146)
It looks like the OP is floating all the parts, as none of the chokes or transformers mounted to the wood chassis' appear to have a discrete protective earth connection to frame/core. OP, have you con .......
177: Tubes Asylum, RE: circuit for creating semiregulated DC for heaters, very little waste heat (0.00)
Posted by trobbins on 2018-09-18, 22:21:12 (110.145.182.146)
What is the ripple voltage on the heater supply for an example valve? What is the change in heater warm up time for a typical valve? What is the change in power factor of the supply AC - the supply cu .......
178: Vintage Asylum, RE: Restoration voicing of vintage amplifiers (0.00)
Posted by trobbins on 2018-09-14, 03:53:07 (119.17.152.52)
I think you are fooling yourself if the sound of the amp is going to recreate the same sound 60 years ago - that would be the domain of the speaker - are you using 60 year old speakers/cones/magnets/e .......
179: Vintage Asylum, RE: Mystery Vintage Power Supply (0.00)
Posted by trobbins on 2018-06-22, 01:11:28 (119.17.152.52)
13.8V is a common float charging voltage for VLRA 12V batteries, and 12Vdc equipment powered with a battery backup capability - that's its most likely original application imho. .......
180: Vintage Asylum, RE: Help Identifying Vintage DIY EL34 Amps (0.00)
Posted by trobbins on 2018-03-17, 21:07:50 (119.17.152.52)
Can you check if the chassis mounted adjust pot and cathode circuitry is the same as the ACRO Williamson circuit they used to show off the TO-300 - see link. Pretty much have to cross-check the preamp .......
181: Vintage Asylum, RE: Homebrew Amp? (0.00)
Posted by trobbins on 2018-03-10, 14:25:34 (119.17.152.52)
"The small interstage is limited to 3k bandwidth because we want it strictly for voice and stay within the legal limits of AM voice response." I'm guessing that is a typical response commonly used for .......
182: Vintage Asylum, RE: Homebrew Amp? (0.00)
Posted by trobbins on 2018-03-09, 21:12:51 (119.17.152.52)
Yes the smallish 807 driver transfer driven SE by the 7 pin valve (pentode) is unlikely to have a wide frequency response, but there is room there to modify the preamp stages as you wouldn't be starti .......
183: Vintage Asylum, RE: Eli, all I have right now is (0.00)
Posted by trobbins on 2018-01-23, 02:30:10 (119.17.152.52)
If using with a PT secondary above circa 350V-0-350V, and considering GZ34 450V rating, it would be safer to use two UF4007 in series for each anode - if the valve goes gassy then the ss diodes should .......
184: Vintage Asylum, RE: Radio Craftsmen 500 (0.00)
Posted by trobbins on 2017-05-07, 06:16:24 (203.219.211.250)
If you have a megger, then could be worthwhile checking for insulation leakage current at say 500VDC to the can in the 4uF - that could save your transformer and rectifier one day. .......
185: Vintage Asylum, More photos please (0.00)
Posted by trobbins on 2017-02-17, 15:37:57 (203.219.211.250)
I'd certainly appreciate any underside photos. And if you get adventurous then any detailed photos of the transformers and chokes that may show their origin (eg. Partridge models) - but that detail ma .......
186: Vintage Asylum, RE: "Genuine D. T. N. Williamson Amplifier", what do I have here? (0.00)
Posted by trobbins on 2017-02-17, 05:07:09 (203.219.211.250)
Some amplifier history in link, from: http://dalmura.com.au/projects/Williamson.php .......
187: Tube DIY Asylum, RE: What this country needs is a good 3-5Hy choke... (0.00)
Posted by trobbins on 2013-12-25, 15:55:05 (101.173.42.168)
Ahh well, there was a tinge of assumption that you were referring to NA, which is why I more explicitly referred to 240VAC so that anybody overseas from where I live would not get confused. Flouro ba .......
188: Tube DIY Asylum, RE: What this country needs is a good 3-5Hy choke... (0.00)
Posted by trobbins on 2013-12-24, 22:59:22 (101.173.42.169)
If you lived in a 240VAC country and needed to quickly check performance, then strangely enough a ubiquitous 18W flourescent light ballast gives about 1.8H with about 50 ohm DCR and maintains inductan .......
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