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1: Re: underbiasing / overbiasing of tubes. Will it damage tubes, circuits? (9.26)
Posted by steven oda on 2004-01-09, 18:32:22 (24.205.10.224)
AM, Warning, un-professional response: 1.) Under-biasing the power tubes can make them run hot and shorten their life. Usually, you can tell by the tone of the amp, especially when cranked. Amps tend .......
2: Re: How to bias (9.26)
Posted by bmotorcycle on 2006-06-25, 12:54:28 (216.155.219.51)
We all were new to the tube scene at one time or another. biasing means that you are supplying the power tubes (without knowing what amp you have, they are usually the big tubes) of a power amplifier .......
3: Re: biasing kt88 (9.24)
Posted by Julien M. on 2001-01-21, 17:45:44 (63.23.133.199)
Randy, I've used many different power tubes in my Jolida 502b (now out of my system). I believe Jolida recommends 50mV (+/-5%) per tube instead of 5mV. That's what I used with all power tubes with goo .......
4: To someone who know Scott 222c (9.12)
Posted by TomJones on 2000-09-12, 02:04:09 (153.20.24.68)
I would like to find out more about the biasing for the power tube. According to the web site of H.H. Scott, the biasing of the amp is FIXED. What does this means? Just change to the new power tubes a .......
5: RE: Biasing tubes (9.06)
Posted by truep on 2008-12-03, 13:07:42 (173.71.4.132)
You only bias the power tubes, the driver tubes are self biasing. .......
6: PS (8.76)
Posted by gadsons on 2002-01-01, 18:30:52 (64.252.65.97)
The BATs are also much easier (and cheaper) to maintain. The power tubes are each self-biasing so matching is not as important and you don't have to go through the VT-100 PIA biasing procuedure. ::: T .......
7: Re: Not biasing power tubes after rolling them ,will..... (8.39)
Posted by Mike Bates on 1999-11-26, 15:33:06 (204.210.193.104)
If the amp is self biasing no, otherwise you should rebias.. Mike Bates .......
8: Re: biasing and old power tubes etc. (8.07)
Posted by Tom Bavis on 2007-02-07, 11:06:21 (65.116.131.6)
If you can buy 8417s for $5 apiece at the corner TV shop... bias it at 110-120 mA and you'll get a little more power, a little less distortion. Have you checked the price of 8417s lately? Biasing at .......
9: jadis defy 7: help!!! (8.05)
Posted by galnat on 2003-12-29, 03:12:46 (62.11.145.192)
I’m desperate…I own a Jadis Defy 7 (mkI, I believe, buyed on 1994): could anybody point out me like upgrade it to the latest version? Besides, anybody could tell me if my model is self biasing? I have .......
10: Re: Question....thanks (7.92)
Posted by walter on 2005-03-09, 10:51:17 (206.116.21.212)
"Power tubes with high'ish gm or emissions can give them a challenge." Same here, power tube (KT88) with around 80% life seems work better than brand new tube, I mean more stable with biasing, on my P .......
11: Will Biasing a tube too high shorten its life ? (7.90)
Posted by vinylbee on 2005-04-15, 07:40:50 (171.159.192.10)
I am new at biasing tubes and instructions with my Jolida 502 indicate it could be within a certain range. I chose to bias them within the middle. Just curious to know if i had it biased to the top of .......
12: Re: HELP ! on Sherwood S-5500II Tube amp (7.83)
Posted by steve oda on 2003-09-19, 18:52:07 (66.214.160.49)
Dave, Check the idle bias and B+ onto your power tubes. Even if you have auto-biasing, the circuitry operating the biasing may be out of whack. Those "halos" could be a result of overheated tubes. Do .......
13: Re: Biasing Carvin 100 Power Amp (7.80)
Posted by corerosin on 2005-08-15, 05:34:07 (65.146.213.177)
Yeah, I don't know why manufacturers are reluctant to provide biasing information to buyers of their amps. Perhaps it's because their customers are guitar players, and are consequently nuts. I don't m .......
14: Biasing Tubes....how the heck!!! (7.75)
Posted by Marty on 2000-04-25, 21:44:15 (203.97.2.251)
Hello....I'm seeking advice on how to bias your tubes. Are there any articles on the Web where I can get help?. Basically I have a number of questions: a. Is it for both Power and Pre tubes? b. What a .......
15: Re: What is rolling and biasing? (7.59)
Posted by will on 2000-12-15, 07:44:21 (208.59.41.137)
Hello, I do not know what rolling is although I would guess it is just trying different tubes for different sonic signatures (others please correct me if I am wrong). The easiest way to explain biasin .......
16: Tube Bias (7.58)
Posted by longtimer on 2009-02-11, 11:46:48 (160.36.191.151)
Curious about something I read on Kevin Deal's Upscale Audio website. Under "Tubes" and "Frequently Asked Questions" the text states: Before plugging in your fresh new set of power tubes, you must tur .......
17: How to bias (7.55)
Posted by HamoverV on 2006-06-24, 20:30:24 (71.208.229.219)
So I'm in a process of playing with different tubes for the first time. What exactly is tube biasing? Is this something I can do without any special equipement? What is the importance? And does it mat .......
18: There is a confusion re. what is under- and what is over-biasing. (7.49)
Posted by sser2 on 2005-08-05, 18:54:20 (128.125.179.129)
To my understanding, underbiased means too little negative voltage on g1 which causes too high a current through the tube. High current is good thing because the tube operates more into class A and be .......
19: 60 to 100wpc mono blocks for around $1000 to 2000... (7.47)
Posted by tube Tom on 2014-04-05, 22:22:43 (67.142.175.23)
that take various power tubes? I'm looking to upgrade from my Quicksilver Mini mites to something with more power & put the Mites in the spare room. The thing is i like the fact that the Mites can tak .......
20: RE: ideal biasing for VTL Tiny Triodes SE (7.36)
Posted by Palustris on 2010-07-20, 08:30:05 (24.128.56.196)
If I recall correctly this is a small PPP EL 84 amp, triode connected. When you reduce the current through the tubes, you are biasing the amp from class AB towards class B. If you like the sound, so m .......
21: RE: Biasing (7.21)
Posted by Tom Bavis on 2023-06-01, 07:52:35 (98.3.112.80)
Preamp tubes use self-bias - no adjustment needed. They operate at a small fraction of their power rating and signal voltage, so small deviations from optimum are insignificant. Power tubes can use s .......
22: Question about biasing EL34's (7.14)
Posted by longtimer on 2009-01-02, 07:49:10 (160.36.190.250)
My question concerns biasing power tubes. Does bias effect sound and tube life or just tube life? As long as you are within the manufacturers " bias range" setting would minor tweaks to the bias resul .......
23: RE: biasing power tubes (7.00)
Posted by R. Mercure on 2011-11-13, 02:54:53 (74.107.168.54)
"Output" tubes (a "power tube" is ANY tube that passes considerable current including rectifiers, regulators, etc. - common but sloppy terminology) are typically biased in a "static" - no signal -and .......
24: Re: Self-biasing tube circuit, can somebody explain further please (6.99)
Posted by KlausB on 2000-12-11, 07:53:55 (141.76.249.2)
One cannot say fixed bias is the good one and self biasing is the bad one or vice versa. Self bias: grid has ground potential, cathode has + potential, controlled by the tube current and resistor valu .......
25: Re: Couple of Different Questions (6.98)
Posted by steve oda on 2003-09-20, 12:37:22 (66.214.160.49)
Paul, Depending on the the type of biasing control---whether each power tube has a bias pot, or each pair of push-pull has one bias pot, or there is only one bias pot for all the the power tubes, will .......
26: Re: biasing tube amps (6.98)
Posted by MIchael Samra on 2005-08-06, 03:10:22 (66.188.56.2)
There is a lot of schools of thought at work here.I always found if you have a nice power supply with little or no sag on a PP amp its better to bias in class AB.I think you mean by underbiasing the t .......
27: RE: Biasing KT88 and increasing output power (6.88)
Posted by Tre' on 2012-10-02, 10:22:26 (75.82.52.72)
If by "more bias" you mean more negative bias voltage resulting in less idle current flowing in the output tubes, then it means less Class A power but more total power. Tre' .......
28: 6P14PEB is... (6.80)
Posted by sser2 on 2005-10-30, 21:41:56 (128.125.179.129)
not exactly 7189 according to data sheet. It has lower max plate and screen voltages. However, these tubes stand very well under hard conditions. In my Scott 222C I run them 450 V on plates, 360 V on .......
29: RE: Tube biasing in the 21st century (6.77)
Posted by perceptiveengineering on 2012-10-16, 20:38:44 (97.125.171.44)
Power line voltages tend to be higher now than they were way back when. Proceed accordingly. No one would ever accuse any of the Dynaco designs of being hard on power tubes. That's why there are a lot .......
30: Re: automatic biasing circuit, does it mean... (6.75)
Posted by steven oda on 2002-01-06, 22:46:57 (24.205.9.166)
TW, True "auto-self biasing" has circuitry to set the idle point depending on the various power tube's electric characteristics. This isn't to be confused with self-leveling, which some folks refer t .......
31: Re: Tube biasing question (6.72)
Posted by Laudanum on 2003-04-16, 18:14:57 (4.62.216.40)
Thanks ... I think. See, my smarts are definitely lacking in this area (i AM the dullest tool in the shed) so maybe I got 1/2 of what you are explaining. The tubes were purchased from Triode and I am .......
32: Re: Cayin A-88T (6.69)
Posted by afg on 2006-07-06, 21:46:30 (203.197.43.50)
Sorry to hear about your case. I can understand your situation since I too went through the same. I broke a tube while cleaning it (really really stupid of me) and I had to send the amp to the dealer .......
33: RE: Onix SP3 tubes and biasing... (6.65)
Posted by catama on 2013-12-04, 21:38:31 (69.42.25.96)
Still have one, but it is boxed up. When I was using it, I replaced the 5881's with 6GL6's and replaced the 12AX7 tubes with 5751's. You have to set the bias different if you replace the power tubes. .......
34: Re: Looking for Jolida SJ501A owners. I have some basic questions. ( I used the search function first!) (6.62)
Posted by analogmaniac on 2000-02-20, 18:46:40 (209.240.200.55)
You can call Jolida for your owner's manual. Those folks are pretty helpful & friendly. Depending on what power tubes came with 502A, you can bias your tubes accordingly.It is usually prudent to bias .......
35: Biasing question...KT-66 (6.59)
Posted by Audiodyssey on 2008-10-28, 18:14:31 (76.87.203.184)
Hate to ask first grade questions here, but I am in first grade!!! I have a ST-70 with the VTA Board and also with the Triode Power transformer upgrade, which supplies the extra current for the KT-66 .......
36: Re: Always Thought If You Couldn't Find 'Bias' Pots On Tube Gear, It Was "Auto-Biasing" !!?? (6.58)
Posted by steven oda on 2001-11-02, 13:50:23 (24.205.10.75)
John, Could be cathode-biased. These are self-leveling (like most front end tubes are cathode biased) to a degree. For power tubes you may need to change out the cathode resistor between vastly differ .......
37: Curiosity: Resistor Problem (6.58)
Posted by GEO on 1999-09-10, 09:03:48 (204.146.164.129)
What would be some of the problems associated with a bad resistor in a power amp. Would there be obvious distortion? Would there be a problem in one of the channels. If the amp is manual bias, there .......
38: RE: Biasing voltage for Precision Fidelity M7A (6.56)
Posted by FenderLover on 2009-10-02, 19:58:30 (24.205.13.241)
I couldn't find the schematic. What power tubes do you run? What Class is the amp (Class AB1, Class "A")? And do you know what the plate voltage applied to the anode of the power tubes is? From these .......
39: Global Neg Feedback and biasing (6.52)
Posted by FenderLover on 2009-03-14, 18:03:08 (24.205.135.52)
Steve, Had a question on theory of GNFB operation. My understanding is that amps which have GNFB to an earlier pre-amp or gain/PI stage can actually cause problems with amps which are over-biased to t .......
40: Re: KORA Design 30 help-which tubes go where?- (6.52)
Posted by caa on 2003-02-07, 22:04:33 (24.185.80.22)
the Kora design 30 uses 4 EL34's as power tubes on the left and right. The driver and input tubes (3 of them) are in the center and should all be identical. Make sure the power tubes are matched, at l .......
41: RE: Biasing KT88 and increasing output power (6.50)
Posted by perceptiveengineering on 2012-10-08, 19:52:28 (97.125.171.44)
If the power tubes bias up the same and you have that big a difference in output from one channel to another, the problem is upstream of the power tubes. Unless one of your output transformers is hose .......
42: trying other tubes (6.49)
Posted by FenderLover on 2009-04-09, 17:34:15 (24.205.130.19)
Is Manley's tech suggesting that you keep trying different tubes? Because in my experience this may not be the best approach. Blown power tubes and B+ main fuses are an indication maybe something inhe .......
43: Not biasing power tubes after rolling them ,will..... (6.45)
Posted by Bob Meyer on 1999-11-26, 15:15:09 (12.23.161.3)
that usually cause early tube failure? .......
44: RE: Would a sign of power tubes wearing out.... (6.45)
Posted by FenderLover on 2009-11-21, 10:30:20 (24.205.133.184)
JOC, when was the last time you checked the bias? Too cold (or over-biased) power tubes also lack bass and have poor transient response, too. It the amp still sounds tired and has poor response, after .......
45: RE: Old radio, sweet tubes (6.42)
Posted by FFlump on 2010-03-20, 09:37:19 (84.202.60.159)
I tried it yesterday with new tubes. It worked for 5-10min but then there were some sparks from within the power supply and smoke came out. Needless to say I nabbed the power chord mighty quick. I don .......
46: Re: importance of biasing tubes (6.42)
Posted by LR-dan on 2007-04-11, 11:10:03 (68.75.162.241)
If your manual has pictures and schematics you can figure out if your bias is measured as a voltage drop across a resistor. The bias current is equal to the voltage you measure divided by the resistor .......
47: Re: Newbie needs to understand tube terms (6.39)
Posted by J Harkin on 2000-11-29, 18:02:11 (24.218.233.232)
Is tube biasing optional? Or is it one of the innumerable things that can be done to fine tune your system. Biasing is not optional. If the amplifiers design has bias controls, they should be adjust .......
48: Re: YOUR POST ABOVE is IMPORTANT !!!!!!! (6.37)
Posted by Tre' on 2005-11-09, 18:04:52 (68.123.156.128)
Technically, higher bias lowers total output power. If you bias your output tubes into Class A/B, in a PP amp, you can get much more power than biased all the way to Class A. I think some may prefer C .......
49: Tube amps in storage HELP! (6.37)
Posted by artto on 2002-11-24, 13:57:07 (12.249.14.48)
I have some Luxman MB3045 monoblocks that are now using Gold Aero 8045G output tubes. A number of years ago I had these amps in storage for a few years. When I fired them up, one by one the output tub .......
50: Re: Jadis Biasing Help (6.36)
Posted by SBK on 1999-08-04, 18:46:29 (161.142.78.80)
Hello. I too am an owner of such Jadis Orchrestra unit. I too was not told by Jadis dudes how to re-bias and my dealer too says that I don't need to re-bias. Got to a point where I was really pissed o .......
51: Re: Found a good non-technical explanation of bias and power tube matching (6.35)
Posted by desert dweller on 2006-08-30, 13:12:58 (68.0.154.245)
Very interesting discussion. I just started a new thread after having problems biasing a new quad of power tubes that was burned in by the dealer for 72 hours (and matched). Don't know yet if there's .......
52: Autobias for 6L6/EL34/KT88 (6.35)
Posted by SWMoore on 2003-03-31, 17:48:57 (12.222.22.209)
I have a quest: to build a push-pull output stage capable of handling mismatched tubes that I can audition 6L6, EL34, and KT88 tubes working in ultra-linear, triode, or pentode mode in class AB operat .......
53: RE: Power tube types, Sound differences? (6.33)
Posted by mjcmt on 2008-12-20, 07:52:04 (168.215.131.150)
I'm not sure I can answer all your questions. Cary told me the transformers are new and excellent so the amp can be used w/ 2-32 speaker loads from the one set of speaker taps. I read that the inner .......
54: DIY yaddy-yaddy (6.31)
Posted by steven oda on 2001-11-07, 20:36:52 (24.205.10.75)
J2, I mentioned DIY'ing, not just for the hobby aspect---but you learn a lot about what "voices" a unit. The caps and resistor in the front end play an enormous role in the final tone of any pre-amp o .......
55: 6CA7/EL34 Tubes & Audio Research Power Amps (6.30)
Posted by XLR8OR on 2009-10-29, 21:13:41 (138.25.85.111)
Has anybody successfully used 6CA7/EL34 tubes in place of 6550's in ARC power amps? I gather biasing them under a maximum value of 55 mV would be feasible. Any comments would be gratefully appreciated .......
56: HELP. Jolida won't bias!! (6.27)
Posted by Dan Lyons on 2002-07-13, 16:45:32 (198.81.17.174)
I finally got some new power el84 tubes for my Jolida 102b. I've used the stock power tubes up to this point. I switched them out for some new EI's today and proceeded to do the biasing proceedure as .......
57: Re: Help on biasing an EL34 amp (6.26)
Posted by steven oda on 2003-06-04, 10:36:42 (24.205.12.219)
AP, Have you ever biased an amp before? Kinda got a general idea as to why you do it & what is involved? Are these FIXED BIASED Class AB1 amps? With direct ground straps from the power tubes' cathodes .......
58: Re: How do I bias my tubes...or Best Book to learn about Tube Audio & tubes biasing ? (6.26)
Posted by CR on 2004-11-19, 06:43:35 (129.42.208.182)
Ooooh, I wasn't even aware of that basic fact. Thanks for educating me on that. Well, I have a Dynaco PAS-3 pre-amp, a Dynaco ST-70 power amp, and a Heathkit AA-121 power amp. Later. .......
59: RE: Biasing problem with Dynaco MKIV (6.23)
Posted by Jim McShane on 2012-03-10, 07:36:55 (24.15.32.233)
One of two things is occurring: 1. The plate voltage at the output tubes is lower than it should be. This could be due to out of spec resistors, tired can cap, etc., something in the power supply. Che .......
60: Re: biasing CJ MV60; sound effects (6.22)
Posted by Lynn on 2002-10-01, 15:15:28 (207.168.141.211)
Hi, I am not sure, but I would think that the red light indicates an overpower condition. So, if one wanted to over bias leaving the light on would indicate that condition. I am fairly new to tubes, b .......
61: Biasing (6.19)
Posted by Doug O. on 2001-06-03, 22:08:28 (207.172.11.232)
Does anyone know of good way to bias power tubes? Are there any good inexensive aids out there? .......
62: Re: What causes an amp to sound forward or laid back? (6.18)
Posted by steven oda on 2002-07-06, 10:31:29 (24.205.20.241)
Francis, The Million Dollar Question. I'd look at those gain stage and phase inverter tubes, first. Then, the power tubes. What types of tubes are you using? The next thing is the voltage onto the pla .......
63: Biasing Fisher amp - can anyone shed light on this? (6.17)
Posted by PeterI on 2007-03-11, 21:41:04 (71.212.175.19)
I have a Fisher tube amp, number 680-A from a console. I am starting to restore it; it has 4 - 7591 power tubes. I have not touched the bias adjust or the 2 "AC balance" screws on top of the chassis, .......
64: RE: Can anyone here tell me about their thoughts on these tube amps (6.17)
Posted by Charlez on 2007-11-18, 13:18:20 (76.14.38.153)
I concur with the positive comments about the Jolida 801A. I recently acquired mine used (2yrs.) in first-rate condition on eBay for about $700, and am very pleased with it. Unlike earlier models that .......
65: Re: Do i need to "rebias" if I roll my tubes? (6.17)
Posted by OceanRoar on 2003-08-25, 13:25:51 (208.0.20.2)
Biasing tubes usually applies to the power tubes in amplifiers. Does not apply to the small signal tubes in your preamp. .......
66: On biasing, how often? (6.16)
Posted by jseverino50 on 2012-01-10, 23:09:51 (121.54.29.21)
How often should you bias power tubes? What's the ideal bias reading? .......
67: Biasing (6.15)
Posted by itolduso1000timesb4 on 2023-05-31, 04:22:13 (65.92.230.222)
Why do power tubes need to be biased and why is it that pre-amp tubes are ready to go once installed in the socket? Yes this is an admission of my limited knowledge of basic electronics! Thanks! ::: .......
68: RE: Tube Bias And Sound (6.13)
Posted by Mr_bill2 on 2011-11-03, 06:27:05 (108.56.69.254)
Just out of curiosity, why did you want to listen without biasing first? Most tube power amp manuals warn against running new tubes without biasing upon initial installation. I hope others more knowle .......
69: SF Power 2 - biasing help please! (6.13)
Posted by MIKEA on 2001-11-19, 18:19:40 (152.163.204.194)
Hi everyone:. I am new to tubes and have a situation that's not covered in the owner's manual. My Power 2 is approximately 2 months old. I tried to check the bias tonight and am having a problem. All .......
70: Re: Here's the scoop (6.10)
Posted by Smoke-Test on 2004-02-11, 16:38:54 (64.163.104.6)
Burn in is not really much of a factor on small signal tubes. It is more of an issue with power tubes. As power tubes cycle and age, there are critical changes than can take place. These ususally invo .......
71: Re: Do the power tubes have same impact ? (6.10)
Posted by Mechans on 2007-02-16, 04:44:26 (68.46.108.249)
The descriptors all make sense to me except bloom, if your tubes were simply burned in . The loss of all that would be a result of premature aging due to ? over biasing. What about the input tubes and .......
72: Not really. (6.09)
Posted by sser2 on 2004-03-10, 17:18:56 (151.195.211.185)
There are two ways of biasing output tubes. One is automatic bias. The source of bias voltage in this approach is voltage drop on cathode resistor Rk. As the current through the tube increases with in .......
73: bias setting for Luxman 50ca10 amp? (6.07)
Posted by stevefzr on 2000-11-17, 23:15:40 (203.9.148.12)
Hi, I've got an sq-38fd Luxman which runs the 50CA10 tubes. It's the same circuit as the Custom 60 (which I think is the same as the MQ-60). Anyway, the manual is in Japanese so I don't know what to s .......
74: Re: help! power tubes unresponsive to biasing... (6.05)
Posted by steven oda on 2001-08-11, 16:51:42 (24.41.2.12)
Al, Better check the bias power supply circuit to your left channel. Somewhere in the bias circuitry you probably have a dead resistor or cap. You did say you can bias both pairs on the right side? An .......
75: biasing power tubes (6.03)
Posted by mboldda1 on 2011-11-12, 20:46:37 (99.103.204.89)
i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing. which is the correct way? .......
76: Re: Not biasing power tubes after rolling them ,will..... (5.99)
Posted by David Brown on 1999-11-26, 18:08:50 (207.172.139.15)
The simple answer is you can't predict what will happen if you don't bias. If you don't check, and your tube is overbiased, you will experience premature tube failure and increased output. If your tub .......
77: cj premier 140 bias question (5.99)
Posted by Shane from AUS on 2006-01-27, 15:28:46 (211.31.177.135)
I am currently demoing a cj prem 140 power amp. I have noticed when biasing the tubes the bias lights are RED when biasing. Is this normal? When I owned cj prem 8a's the bias lights used to be light .......
78: Re: EL34 tubes (5.92)
Posted by Scott T. on 2000-07-12, 08:45:00 (24.161.8.225)
In the Cary SLA 70B Sig. amp you can use EL-34's,KT88's,6550's,and KT90's.The amp is NOT self-biasing though.You will have to adjust the bias when changing power tubes. .......
79: Re: biasing and old power tubes etc. (5.91)
Posted by razzwill@gmail.com on 2007-02-07, 06:57:50 (60.48.247.115)
Yes Catch22, the GE 8417 mono amps are supposed to be Class A. What they are now I don't know! Sounds great though. If you are familiar with the Quicksilver GE 8417 amp——there are two transformers, on .......
80: RE: ARRHHGG!;-) (nt) (5.89)
Posted by Mendel on 2010-02-05, 05:48:03 (173.32.12.222)
Hi Twystd: Just a note on biasing. I dont think you can say universally to bias at 45ma--it depends on the amp. In my Rogue, I dont even bias KT88 that high. The recommended bias for KT88 is 40ma, and .......
81: RE: biasing power tubes (5.89)
Posted by mboldda1 on 2011-11-13, 11:00:29 (99.103.204.89)
this is what the manufacturer says: " set the volume at lower level (less than one quarter). i guess you could take this as no signal present or with a signal. .......
82: Re: Life span of EL34 tubes (5.88)
Posted by foolno1@blazenet.net on 2003-04-27, 02:44:31 (63.174.237.88)
The life span of any power tube used for audio will depend almost entirely on the circuit it's used in. Over or under biasing outside the window of correct bias currents can shorten tube life as well. .......
83: Nomenclature (5.87)
Posted by steven oda on 2001-12-26, 18:53:45 (24.205.9.166)
Joly, This is one of many "word games" played in the world of electronics. "Fixed-bias" means that the tube has a preset negative voltage on the controller grid. This negative voltage inhibits flow of .......
84: Re: biasing question(s)... (5.87)
Posted by MIchael Samra on 2005-05-04, 15:38:10 (66.188.56.2)
Is this bias current in milliamps your speaking of the 43 and 48? If it is your not biased enough for the tubes to produce full power in most PP amps. .......
85: Re: Heater voltage & Biasing (5.87)
Posted by Carlos on 2001-01-29, 09:05:31 (200.192.203.168)
Heater voltage does not directly affect cathode bias in most 6.3V tubes, because they are indirectly heated (cathode separate from heater). However, it will reduce total emission, the tube will have l .......
86: Re: Tube Biasing (5.87)
Posted by robber on 2005-09-07, 13:41:20 (12.160.195.66)
I would be weary of a dealer who will not bias an amp, especialy one they sell! I am not familiar with the unit in question but I will assume that it does not have built in meters to make biasing REAL .......
87: D70 Output Tubes Drifting WHILE Biasing (5.86)
Posted by Jonesy on 2014-03-22, 16:17:10 (50.72.198.229)
My bias on the 6550C tubes used to be easy to set. Never drifting much upon check ups during the year, always near the 65 mark. Last time I checked, I was not able to even get a steady reading. It was .......
88: RE: 6CA7/EL34 Tubes & Audio Research Power Amps (5.86)
Posted by Michael Samra on 2009-10-29, 23:10:16 (97.84.146.37)
Has anybody successfully used 6CA7/EL34 tubes in place of 6550's in ARC power amps? I gather biasing them under a maximum value of 55 mV would be feasible. I actually tried el34s in the mac mc60s an .......
89: RE: D70 Output Tubes Drifting WHILE Biasing (5.86)
Posted by Jonesy on 2014-03-28, 08:47:15 (207.134.250.139)
Hi Mike, I would like to remove some tubes as you suggested. So I would leave in the output tubes, the power tube, and the 12ax7 that is part of the power supply. Take out 2 driver and 1 signal tube p .......
90: Bias Power supply (5.83)
Posted by steven oda on 2001-06-17, 14:40:48 (63.23.91.228)
Hogy, This amp is self-biasing? And normally uses KT-88's? Maybe the bias circuit is failing or the bias power supply is a bit hincky. Have you tried the original KT-88's back in the amp? Any problems .......
91: I'll add a few... (5.83)
Posted by Sector-7G on 2004-01-09, 19:20:05 (130.203.161.119)
To take some of Steve's starters: 1.) Under-biasing the power tubes can make them run hot and shorten their life. Underbias, to adjust the grid more positive. Results in higher dissipation. Depending .......
92: Re: music ref. rm-9 low level hum help! (5.81)
Posted by Juergen on 1999-11-01, 22:16:27 (203.127.114.190)
I assume you are talking about the Mk 1. Maybe you can try to get a Mk 2 in the second hand market. Mk 2 is very user friendly, really reliable, reasonably well made (of course not in Cary Audio's cla .......
93: Re: biasing and old power tubes etc. (5.80)
Posted by Rob Mercure on 2007-02-08, 08:08:53 (71.254.42.199)
I would be suprised if an amp was designed to use 8417s in Class A - while stranger things happen t'would be a odd choice. Rob .......
94: Copland CTA-505 Power Amp (5.79)
Posted by steven oda on 2000-08-25, 18:28:00 (63.23.86.238)
What is a good range to bias the Svetlana 6550C tubes in the Copland CTA-505 Power amp? Plate voltage is 415 volts. Amp in tetrode mode. Any experiences with lifetime expectancy and/or changes in tone .......
95: Re: Non-match power tubes (5.79)
Posted by steven oda on 2002-07-22, 13:29:56 (24.205.20.241)
Steve, So you've had supposedly "matched" tubes go ballistic---because only the Gm matched, but not the other parameters stated? How do you compensate for this when the tubes "break-in" or start to we .......
96: The Rogue power tranny has plenty of juice for KT90... (5.78)
Posted by ducati on 2006-01-30, 05:35:31 (216.235.16.22)
...according to Mark @ Rogue. I ran KT90 in my Tempest II (essentially a Stereo 90) with good results. I had a good quad, though, and didn't have the biasing issues you did. In fact, I ran them at 55m .......
97: LOL, I've never seen the blue/purple glow, but...... (5.76)
Posted by Chuck Y on 2008-09-17, 12:19:57 (4.245.111.85)
I've sure seen the 'light' show that must be following. Quite amazing. Happened just once after biasing up new tubes to munfacturers spec's. Lowered the bias setting 5ma and has never happened since. .......
98: Biasing Carvin 100 Power Amp (5.70)
Posted by Bluebird_12 on 2005-08-14, 17:09:58 (142.177.207.92)
Hi, although it is a guitar amp, I use it for hi-fi and can't find any info on how to bias the power tubes. I have emailed Carvin asking for information with no success. Any help would be greatly appr .......
99: Heathkit amp problem (5.68)
Posted by Face on 2008-06-04, 23:34:10 (69.117.222.160)
Recently, upon startup, my preamp tubes and rectifier tube will light up quickly and brightly, with the power tubes lagging behind. Once the power tubes illuminate, a hum starts in my speakers and pro .......
100: Input bias on ARC VT100Mk2 (5.68)
Posted by Vinylbob on 2001-10-17, 20:50:11 (162.33.244.157)
Dear Abe, There is an adjustment for the driver tubes that is not noted in the manual for the Mark 2. Talk to Chris or Leonard at ARC. It is not simple like power tube biasing. .......
101: Groove Tubes KT-66HP (5.66)
Posted by steve f on 2002-07-02, 10:28:55 (64.158.250.123)
Anyone know the power rating on the GT KT-66HP? They'll be running at approx. 500 volts. Looking for any recommendations for biasing range. .......
102: RE: Biasing KT120? (5.66)
Posted by casouza on 2011-08-19, 00:39:05 (186.205.212.130)
Also, increased output tubes bias by 60% may require mods to the bias power supply or may damage the output transformer if there is any momentary imbalance between output tubes. .......
103: Re: Setting Bias (5.66)
Posted by steven oda on 2001-02-19, 11:42:48 (162.119.232.100)
Also depends on topology of your amp. Whether Class A push-pull or Class AB1 push-pull. You need to find specific recommended values for your amp. Also, you'll need to know if the amp is Cathode Biase .......
104: RE: Newbie question: How often does the bias need to be set/checked on a tube amp? (5.65)
Posted by tube Tom on 2014-08-20, 14:20:32 (67.142.175.27)
Hi Jim, you may have noted the post below that I'm getting (gotten) my first set of manual bias amps? I pretty much figured changing power tubes would require re-biasing, but what about rectifiers? I .......
105: Re: Help: strange problem with new tubes (5.65)
Posted by steven oda on 2001-07-06, 01:43:37 (24.41.64.152)
BB, I'm not familiar with your amp. Is it self-biasing? I recall someone, somewhere saying not to do what you've done. Something about causing an imbalance in the bias circuitry---especially, I'd imag .......
106: Some like it hot! (5.63)
Posted by foolno1@blazenet.net on 2002-08-18, 02:56:41 (24.104.67.54)
Remember that great flick with Marilyn Monroe, et at? Anyway, to answer your question, the design of the amplifier will largely determine how hot the transformers get. Some under-sized power supplies .......
107: RE: Biasing KT88 and increasing output power (5.61)
Posted by griffithds on 2012-10-05, 12:22:35 (69.5.227.25)
Alex, If what you are truly after is a more centered sound presentation, try swapping your 4 output tubes around. There is a lot more going on in a output circuit than just output tube bias . ::: TOPI .......
108: Re: importance of biasing tubes (5.59)
Posted by oocella on 2007-04-11, 09:56:10 (71.105.109.88)
the amp is a Luxman LX-33 I could clearly hear the difference between min and max settings of the bias on the power tubes. I put it right in the middle which sounds fine and is marked as factory defau .......
109: Re: Two seperate bias controls (5.57)
Posted by steven oda on 2001-11-25, 00:38:10 (24.205.13.13)
KT-66, WAG, on my part, but the 6Y6 may need biasing, separate from your KT-66 power tubes. You have a schematic that you might be able to email to me? It'll help (I hope). steve .......
110: Re: When in doubt - rebias (5.55)
Posted by steven oda on 2005-03-31, 16:03:42 (24.205.11.235)
G, I probably mis-understood your post, but I've found tubes don't really age "linearly." Power tubes tend to change most, the first initial weeks they can drift all over the place (putting the Q of t .......
111: Re: Plate dissipation & tube rolling (5.53)
Posted by corerosin on 2006-01-23, 10:51:29 (65.151.170.197)
Your calculations of the standing current in your amp are correct. The screen voltage, although it's current draw will participate in the total current draw, can be ignored for biasing. I should ment .......
112: Dosen't appear to be so super (5.52)
Posted by Chris O on 2009-02-25, 14:30:48 (199.82.243.71)
I would not be overly cavalier leaving Chinese "super" tubes on overnight un-attended, or any power tube for that matter. Once a tube starts drawing excess current due to alignment or any other issue, .......
113: Re: Plate dissipation & tube rolling (5.52)
Posted by tubecrazy on 2006-01-23, 21:41:16 (65.151.95.17)
Much misinterpretation here. Power output and plate dissipation are in NO WAY the same thing. You can get 100 watts from tubes biased at 35 watts idle, or 50 watts idle current. Plate voltage makes p .......
114: Biasing tubes (5.50)
Posted by longtimer on 2008-12-03, 12:48:50 (160.36.190.250)
I tried to do a little tube bias last night on a VTL-ST85 and noticed there are 8 tubes (4 EL34's and 4 12au7's) but only four trim pots. Do the trim pots only correspond to the output tubes? Do you b .......
115: Re: Good power tubes for Rogue? (5.49)
Posted by Cope on 2002-03-30, 15:35:15 (12.30.226.23)
Rogue are self biasing BTW. Most here like the Svetlana 88's, but some report the Penta labs Chinese 88's are steals at $80 a quad. Cope .......
116: RE: These are lovely-sounding tubes (5.49)
Posted by twystd on 2009-01-25, 10:49:12 (66.25.143.145)
I believe these tubes are super under rated for military use, I've heard reports of use up to 650V (rated for 250V) on the plate (not recommended). I've used them in a lot of Fender amps, and so far a .......
117: I have both Jolida and Antique Sound Labs (5.47)
Posted by zorpman on 2002-01-04, 19:23:06 (24.163.107.252)
Both 6550/kt-88 amps. Got the Jolida 801 first, as my first tube amp since my Dynaco 70 days several decades ago. After I threw away all the stock tubes and replaced with USA vt-231 and 5751 drivers a .......
118: RE: Are there Jolida people here? (5.45)
Posted by Netdewt on 2012-01-12, 17:48:35 (76.17.160.152)
I head back from Jolida. They also recommended swapping the power tubes to opposite channels, but first biasing the amp. I have not done it because it makes me nervous poking things into an amp that's .......
119: Re: bought a Cayin A-88t (5.43)
Posted by sgb on 2005-08-08, 09:29:30 (68.225.106.197)
1)I believe this is an auto-biasing amp as one of you'll had mentioned earlier. How can I confirm this? The supplied manual is quite pathetic in terms of details and does not talk about biasing at al .......
120: Re: GTA SE-40 (5.43)
Posted by robert on 2001-10-28, 19:07:37 (64.231.38.170)
I had a Golden Tube SE-40 for a few years. It's a pretty good sounding amp, very tube-y sounding, a good introduction to tubes. It's not PP, it's single-ended parallel. The downside- it eats tubes ali .......
121: Question about fixed-bias power amplifiers.... (5.43)
Posted by AbeCollins on 2005-12-31, 12:47:42 (67.176.116.152)
I read that the McIntosh 275 is a fixed-bias design (not auto bias). What is the difference? Why would a manufacturer choose fixed biasing? Is it more critical in a fixed-bias design to ensure that a .......
122: RE: Question for Corerosin (5.40)
Posted by corerosin on 2007-07-22, 13:38:28 (67.150.53.98)
The stereo/mono switch is gone on my amp, as well. There is, however, a biasing procedure which you must continue if you don't want to burn up your amp. The goal of biasing an amp is to establish a q .......
123: RE: Biasing (5.40)
Posted by 6bq5 on 2023-06-01, 13:09:10 (52.119.121.37)
the manufacturing variances inherent in Power tubes cause output variations by adjusting the bias, the tube can be operated within its sweet spot, a more linear part of its gain curve- when using tube .......
124: Re: Not biasing power tubes after rolling them ,will..... (5.38)
Posted by Dave Brown on 1999-11-29, 04:53:12 (209.49.109.146)
Your manual should provide detailed instructions on how to bias your tubes. It's not a very involved procedure. My Cary's provide a 1/4" phono plug connnected to two wires that I plug into the back of .......
125: Tube matching expert needed (5.37)
Posted by Blues_man on 2005-03-04, 13:45:03 (63.116.189.130)
It's time for me to replace the tubes in my ARC VT100 MkII. If I buy the tubes from a tube retailer, I can get the same tubes that ARC sells for half the price. I haven't set up driver and input tubes .......
126: Power tube biasing (5.36)
Posted by asp6816 on 2009-05-28, 13:48:00 (38.112.120.254)
My power amp uses a pair of 6550 tubes at each channel, the manual tells me to use 2 test points and corresponding trim pot on the PCB and a voltmeter to bias the new 6550s to a specific value in mV ( .......
127: Re: biasing and old power tubes etc. (5.36)
Posted by Catch22 on 2007-02-06, 21:53:55 (4.167.26.78)
I suspect the previous owner converted the amp from Class A to Class AB1 and the amp no longer runs the tubes at the higher bias settings. I would stick with the 45 max negative bias. Are the amps sup .......
128: Tube Rolling (5.36)
Posted by scottsan1@hotmail.com on 2008-12-20, 10:37:50 (88.226.40.228)
I recently purchased my first integrated tube amplifier - Dared MP-60. A push pull auto biasing design rated at 25 wpc. It is driving a pair of 25-year-old Jamo CBR-90 loudspeakers. The sound with the .......
129: Ping: Fenderlover re early 70s Princeton Reverb (5.35)
Posted by dean_martin on 2012-04-24, 15:05:38 (74.45.66.87)
I've had my Fender Princeton Reverb guitar amp since the early 90s. I had it serviced including tube swaps several times when I lived in cities with good amp techs. Now, I live in the sticks and the .......
130: I have the AE-25 basic - not Superamp variant (5.33)
Posted by tville3 on 2003-01-11, 07:03:20 (66.0.82.130)
And it uses 5 "cement power resistors." One is in the power supply (1K 5W) where it drops the B+ down a bit for the screen drive if you run your amp in pentode mode. You don't need the resistor or scr .......
131: Sonic Frontiers Power 2 - HELP... (5.31)
Posted by storelli on 2008-07-16, 17:56:05 (201.86.14.42)
Well, i found a very good deal on a SF2, got home , plugged it to my Shindo pre/Quad 63 and.... glassy/steely/metalic/fu@#$!ing sterile don´t even begin to describe what i´m hearing(i can only imagine .......
132: Re: Audio Research Tube Prices! (5.31)
Posted by Abe Collins on 2001-08-29, 00:43:04 (65.10.208.131)
Thanks for all the comments on tube prices. Are Audio Research power amps self-biasing? Perhaps this is why it is so important to have closely matched tubes? I have a CJ amp (and AR preamp) and I'm n .......
133: GZ37 seems brighter when power tube changed to EML 520B v3 ??? (5.31)
Posted by Jay Buridan on 2014-09-25, 19:21:47 (75.39.16.143)
It may be just in my imagination, but after swapping power tubes from the KR 300BXLS to the EML 520B v3 in my Art Audio Jota HC monoblocks all the other tubes seem to be burning brighter. The Jota is .......
134: Re: what is going on with tube biasing? (5.30)
Posted by Chris Colby on 2000-02-18, 22:54:06 (209.166.187.23)
Thanks for the help. I think I have convinced myself that the amp is in fact defective. The tubes are the correct kind as advertised. I tried biasing the way you described, unfortunately with the same .......
135: biasing and old power tubes etc. (5.30)
Posted by razzwill@gmail.com on 2007-02-06, 20:54:14 (218.208.211.133)
If the bias of an old power tube dips below recommended levels, is it the 'norm' to increase bias on the power amp until it reaches the optimum setting? And we keep doing this until the tube gives up .......
136: There is a difference between "self Biasing" and a robot. (5.29)
Posted by Chip647 on 2015-06-05, 04:50:12 (108.247.77.70)
You still need to measure the operating point when switching tube types. Careful of the high heater draw tubes like the KT120/150 as your amp may not be able to supply the heater current without stres .......
137: Re: Several relevant tube questions! Seeking Answers... [Stereo 70 Related] (5.28)
Posted by steven oda on 2003-06-02, 22:51:07 (66.214.172.141)
Brian, Wandering bias could be poor contact with pins. Resistors or caps within the bias supply which may have cold solder points (did the amp ever bias steady---with other power tubes???). Need to ch .......
138: RE: Thanks (5.28)
Posted by edwyun@hotmail.com on 2010-11-15, 05:40:51 (74.68.57.176)
I remember hearing that, generally, preamp tubes don't need to be matched because, unlike power tubes, they are usually self biasing. But matching (or not matching) may depend on circuit design as wel .......
139: Re: HELP! VT100 MkII 100 ohm resistor wattage? (5.28)
Posted by AbeCollins on 2002-08-06, 16:11:12 (12.252.90.255)
No doubt you're familiar with re-biasing the power tubes once they're in the amp. The smaller driver tubes require a bit more work to get them re-biased. In case you need help, I completely retubed my .......
140: biasing the driver tubes on arc vt100mk1 (5.26)
Posted by mk on 2002-10-31, 21:25:00 (202.166.126.230)
Pls help... recently purchased a used vt100mk1 and thought it was a good idea to replace all the driver/power tubes. After getting hold of two matched quads of 6922(siemens) I could not locate where .......
141: Re: Power tubes for QuickSilver M60s (5.26)
Posted by cruzmsl on 2005-04-04, 19:00:56 (12.219.151.95)
Tom, look on their website under past products. Produced from 1995-1998. They are self biasing 60 watts each. I am mainly looking for comments on the relative differences between the EL34, 6550 and K .......
142: Re: To Scott lovers: Biasing the 299 (5.25)
Posted by Francis S on 2000-11-23, 19:56:09 (202.8.224.47)
Will, I remember replacing the first resistor with a 30ohm/10w. I did measure the voltage drops across each 18ohm and I get about 2.5v and could not lower it significantly by turning the bias pots. Al .......
143: Underbiasing and "running a tube hot." (5.25)
Posted by steven oda on 2002-03-19, 22:24:31 (24.205.19.42)
SG, Sorry, been a bit busy, lately. "Under" and "over-biasing" refers to push-pull FIXED BIAS amps. These amps have a separate NEGATIVE voltage supply fed to the power tube grid via an independent tap .......
144: Mixing Power Tube Brands....... (5.24)
Posted by Scott T. on 2000-05-24, 09:46:01 (24.161.8.201)
As I stated in the General Asylum: I have a Conrad Johnson MV-52 amp that I using Sylvania"Fat Bulb"6CA7's in the front V5 and V6 positions and Yugo"Fat Bulb"6CA7's in the rear V7 and V8 positions. Th .......
145: How does rectifier make a difference in sound? (5.24)
Posted by Spike on 2006-10-20, 16:01:08 (171.71.57.174)
Here's a question for those technically minded... I've read that tube rectifiers in the power-supplies contribute greatly to adding more bloom, body to the sound of the amplifier (or pre-amp). I'm try .......
146: Re: importance of biasing tubes (5.24)
Posted by ooocella on 2007-04-11, 09:12:27 (71.105.109.88)
i just return the bias, ac and dl bal settings to what appear to be "factory default" since it is sort of the medium setting and is marked. Sound is good but I am trying to tweak it by ear with headph .......
147: help! power tubes unresponsive to biasing... (5.24)
Posted by Al on 2001-08-11, 15:26:06 (165.121.73.175)
I've got an Antique Soundlab 1003 tube amp, almost 2 months old. Tubes are ASL-branded EL34's (probably chinese??) The two tubes on the right easily bias to 385mv...with the two tubes on the left, I k .......
148: My quick answer is.. (5.24)
Posted by Quest on 1999-10-12, 16:13:27 (216.18.8.34)
no, not really (my rather naive opinion anyways). This is more true towards Doc's pair of KR2A3. During last VALVE meeting with music playing along we (DOc, Smoothplates, Ed, Richard) had some brief d .......
149: Re: Please help me track down this tube (5.22)
Posted by corerosin on 2006-03-18, 12:45:58 (65.151.164.138)
It worked? That's good news. For what it's worth, chances are that pin 9 of the output tubes' sockets was dirty. That pin is the screen grid of the 6BQ5. When the amp was operating properly the connec .......
150: Re: Svetlana tubes (5.22)
Posted by steven oda on 2002-02-01, 13:53:23 (24.205.9.166)
Newbee, It sounds crazy, but in FIXED BIAS---"overbiased" means too little current flow because you've put too much (or over-biased) the grid negative voltage. Doesn't matter whether each tube is bias .......
151: Re: Biasing - how do I do it and why do I need to? (5.22)
Posted by steven oda on 2001-08-11, 09:02:15 (24.41.2.12)
Horace, I vaguely remember a post about a year ago on this board about Kones amps. I believe they were made in China, HK, or somewhere in the Orient. Did it come with a schematic? If the cathode pin ( .......
152: Re: Need more power than a SET can deliver (5.21)
Posted by Bill Galbraith on 2000-10-29, 13:59:18 (12.78.173.123)
Try the Quicksilver Silver 60's or a used set of the M60's {60 watt mono blocks with auto biasing.. they accept a few types of tubes.} I tried the CJ's and thought they were a little to "tubey" but th .......
153: RE: Tube recommendations- What is best? (5.21)
Posted by Tre' on 2011-02-13, 16:41:46 (69.108.65.81)
"I usually do not like any cathode bypass cap & that includes power tubes. " It's best you stay away from SE amplifiers that use cathode biasing for the output tube and keep all your PP amplifiers, th .......
154: Jolida 1000 integrated (5.20)
Posted by unclestu on 2013-10-27, 22:07:45 (74.87.55.18)
Any one know the biasing procedure for this amp? I see the individual pots and a red LED but there is a second set of adjustment screws for which I do not understand ( haven't opened up the bottom yet .......
155: Re: - - So Were Such 'Small' Amps Designed With "Auto-Biasing" In Mind?? (5.20)
Posted by steven oda on 2001-11-03, 12:22:40 (24.205.10.75)
John, Not sure about 6V6GT amp, but many EL84 amps are cathode-biased. Just like the 12AX7 driver tubes. Cathode-biasing can compensate, up to a point, for different tube current demands and yet maint .......
156: In summary............ (5.19)
Posted by Chuck Y on 2008-02-23, 07:41:39 (4.245.111.45)
Power tubes short out, it is not unusual for this to happen but it is not a common problem. Some power tubes brands are noted for being rugged, SED for example and normally last a long time w/out prob .......
157: Re: VT150 (5.17)
Posted by stash777 on 2002-11-21, 09:22:22 (141.236.81.158)
Ryan, I have an ARC VT130SE and the difference between it and the VT 130 are that it has a somewhat larger power supply, a few upgraded parts and the big difference is that it has a front panel with t .......
158: Re: want full power out of 6l6GC (5.17)
Posted by corerosin on 2006-02-21, 09:35:43 (65.151.156.132)
Thanks for your response. I don't know whether DaveZ is going to respond. He rebuilt the drive section of a ST70 using 4 6SN7's, switched the output tubes to 6L6GC's, and altered the bias supply per a .......
159: Don't forget rectifiers and regulators and... (5.17)
Posted by Maxamillion on 2011-02-16, 10:23:46 (206.228.220.39)
Don't forget rectifier tubes and regulator tubes, they can also alter the sound by changing the operating points of the other tubes. Then you have coupling and power supply capacitors, often noted to .......
160: Re: Non-match power tubes (5.16)
Posted by Steve O on 2002-07-22, 16:20:57 (12.87.58.21)
"So you've had supposedly "matched" tubes go ballistic---because only the Gm matched, but not the other parameters stated?" YES "How do you compensate for this when the tubes "break-in" or start to we .......
161: Re: Question About Matched Quads (5.14)
Posted by steven oda on 2003-03-24, 21:46:14 (24.205.9.230)
MK, Hope I didn't misinterpret your answer... but the original post seemed to talking front end/gain stage tubes. Specifically, the 6922/6DJ8 type duo-triode. Most pre-amp/gain stage sections have the .......
162: RE: New tubes. (5.14)
Posted by dls123 on 2008-02-16, 07:48:26 (207.216.216.94)
Hi Yes, I agree with the other posters. In my experience with 4 or 5 amps and lots of tube types, a small 9-pin like a 12au7 will take only 5 - 10 hours to settle down and reach most of its sonic pote .......
163: Dynaco 70 Bias (5.12)
Posted by John H on 2002-07-21, 04:11:56 (210.254.151.98)
I need a bit of help regarding the output tube bias setup on the Dynaco ST 70. When I set the bias on the bias potentiometer on one channel, which tube am I actually biasing? I can see on the schemati .......
164: RE: Some noob questions about tube bias (5.11)
Posted by TubeAcolyte on 2010-03-08, 07:22:20 (206.132.182.120)
Hmm, all very interesting. I was aware that all tubes don't have current draw, and the differences between fixed or cathode-biasing. I've begun taking in a LOT of information, but it's just difficult .......
165: Re: Heater voltage & Biasing (5.11)
Posted by John Harper on 2001-01-26, 06:48:11 (144.254.108.85)
For small signal tubes, 5V is at the lower limit of OK but is OK. I run one of my preamps at 5V - it has lower distortion and no sign of any problems (with Mullard ECC88s). Remember that heater temp f .......
166: Re: Question....thanks (5.02)
Posted by tvr2500m on 2005-03-09, 13:09:27 (209.6.222.74)
"...their (CJ's) reply is "No experience with such combination but expect biasing problem may occur." Seems to me that's a peculiar thing to say. It's not like the SED KT88, or any current production .......
167: Audio Research VT100MKII Tube Replacement = Hard Work (5.01)
Posted by Abe Collins on 2001-10-20, 22:08:16 (65.10.208.131)
Well, I finally got it right. I replaced all the tubes in my Audio Research VT100MKII and biased the power tubes as described in the owner's manual. What I didn't know until a fellow audiophile mentio .......
168: Re: Not biasing power tubes after rolling them ,will..... (5.01)
Posted by Bob Meyer on 1999-11-27, 08:34:01 (12.23.171.171)
I guess I`m not sure how to do it. I do have an old Simpson voltmeter that still works and an Auto-Ranging LCD Digital Multimeter from the Rat Shack and also have Golden Tube owners manual that have i .......
169: Question on tubes (5.01)
Posted by BR on 2003-03-02, 02:06:27 (12.221.40.219)
Good morning everyone I have a question regarding a flash everytime I power up my integrated tube amplifier. I purchase a set of RFT 12au7 every time I turn the amplifier on I get a soft white flash f .......
170: Re: Do all 6550 power tube amp support KT88 ?? (5.01)
Posted by Zippy on 2001-02-12, 09:45:40 (63.79.77.126)
The heater draw is the same for both tube types. The only real difference is the dissipation rating (35 watts for the 6550 and 42 watts for the KT-88). As long as you do not bias up the KT-88 to pull .......
171: Re: Tube "Warm Up" time? (5.00)
Posted by steven oda on 2002-02-10, 15:50:55 (24.205.19.42)
Peter, I let the amp idle a good 3-5 minutes prior to use. Longer, if the amp has been sitting around and the caps are probably discharged. I usually will let an amp idle for 15-30 minutes before bias .......
172: Re: What is rolling and biasing? (5.00)
Posted by Scott on 2000-12-15, 07:44:08 (206.165.142.131)
Congratulations on your new acquisition Maprik! I am a tube guru with many years of experience and will be happy to give you the benefit of my expertise. In answer to your first question, "what is tub .......
173: Re: The CAV 50 is a Push Pull Class AB design (NT) (5.00)
Posted by steven oda on 2005-01-31, 06:26:57 (162.119.232.108)
CZ, Are you pretty sure the real plate volate is 500 VDC? When biasing, the volume is at zero, no input devices, & speakers are connected, correct? And how long are you allowing the power tubes to war .......
174: Quicksilver Mini-Mite Mono Amp (4.97)
Posted by Luminator on 2000-11-28, 16:26:50 (209.21.65.2)
These cute little amps are $998 for the pair. Using El-34s, they put out 25 wpc, more than you'll ever need. Since they're self-biasing, you can plug in several other tube types, if that's your druthe .......
175: Re: ST-70 biasing (4.97)
Posted by steven oda on 2003-03-27, 12:37:10 (24.205.136.134)
xlz, Amp on, no input, volume at zero, speakers connected. Check the initial reading. Should be close to 1.56 volts. Rough adjust to get to that reading. If you can't get any reading or a reading not .......
176: All your amps are fixed bias... (4.96)
Posted by ducati on 2005-12-31, 14:58:12 (65.24.191.3)
As described below, what you have are fixed bias amps. It is a bit of an odd term, until you realize this only means the bias is "fixed" until you change it--an auto-biasing amp will adjust continuall .......
177: RE: Is it the tube type, or the vintage? (4.95)
Posted by opalize on 2021-09-02, 16:22:05 (128.32.125.82)
The answer really depends upon the bias points in your amp. It is unusual to have a self-biasing amp that uses such a range of output tube types. With that qualification, having experimented with man .......
178: hoe to bias 8417 (4.94)
Posted by wlee on 2005-04-05, 16:03:50 (202.79.92.193)
My power amp is fixed biased with -57 to -27v range with B+ 415v. I had plugged in 6v6 n at 12ma it yielded the best sound for the tube. But I just tried Sylvania 8417 n there is just No sound at all .......
179: Re: KT90 Bias setting?? (4.94)
Posted by Uncle Ned on 2000-06-22, 20:29:22 (199.179.160.241)
KT90 should plug right in & bias up, altho it's not impossible that some might bias outside of the range of the bias control, it's not common. You can get it back in range by changing the 18K resistor .......
180: I have a similar pair of AQ1006DT 105 wpc mono-blocks (4.91)
Posted by zorpman on 2002-01-15, 08:04:23 (12.4.116.34)
After ditching the stock Chinese tubes (replaced with a three 5692 RCA red base driver tubes) and EH 6550 EH power tubes (long breakin but good synergy with the "soft" 5692 drivers) I love this set up .......
181: Re: HELP BLOWN ??? (4.90)
Posted by steve oda on 2003-09-01, 10:15:31 (24.205.12.84)
Pogue, I take it you put a good KT-88 in its place and rebiased it? Unfortunately, a KT-88 can draw a lot of current, espcially if it shorts out. You might want to check grid stopper resistors and swa .......
182: RE: 6n3c tubes in Dynaco ST-70 anyone? (4.90)
Posted by NativePrairie on 2009-08-06, 18:39:52 (98.168.232.24)
I have rolled a ton of tubes in the driver board. I prefer 6cg7/6fq7 instead of 6dj8 and others that work in the Curcio board. The RCA cleartops sound the best, and not by a small amount. They really .......
183: Mesa Boogie biasing (4.88)
Posted by steven oda on 2002-11-03, 08:43:03 (24.205.18.80)
Dave, Not familiar with the stereo version. But, most MB run a FIXED BIAS, with no pot for adjustments. That's why their admonishment to buy "matched" Mesa-Boogie approved tubes. Most of their 6L6GC a .......
184: Re: For Scholl - Biasing your 6B4G's in push pull - What total dissiaption for each 6B4G? (4.87)
Posted by Scholl on 2000-10-31, 08:43:16 (192.135.193.34)
I'm dissipating 22 watts a plate. Some folks say these tubes are good for 30 watts the data sheet says 15 watts. If you want to interchange with vintage tubes go for 15 watts. If you want more power m .......
185: hold the 'phone... (4.87)
Posted by Sector-7G on 2004-08-09, 04:45:45 (130.203.161.180)
That the 12AU7's 'don't need biasing' is a bit misdirected. They are cathode biased, likely with a resistor, bypasssssed with a suitable capacitor. They don't need bias adjustment, that's done automat .......
186: Re: Best PP amp $1500 w/el34s new or used?? (4.84)
Posted by Cut-Throat on 2002-12-21, 15:08:45 (198.81.26.200)
Look for a used Super Amp by Audio Electronic Supply. You can run a variety of Power Tubes in this amp including EL34's. I built my AE-25 Amp for around $600 in kit form. The DJH Super Amp new is abou .......
187: I think you're making a good choice (4.83)
Posted by 1973shovel on 2012-03-13, 15:47:48 (74.177.99.99)
A fresh power supply will help assure your amp will live a long and happy life. The EFB circuit will assure your tubes will do the same, and sound better doing it. I can't guarantee that you'll like t .......
188: RE: And the amp in question provides each power tube with its own bias adjustment... (4.83)
Posted by wiggy924 on 2014-06-04, 09:00:39 (67.0.183.212)
Guys, I popped the Shuguangs SC back in last night and got them warm before biasing to get an overall impression of the two tubes. I can say that the GLs are quite special, images are more palpable an .......
189: RE: Biasing can be a very eary process for anyone..... (4.82)
Posted by scriabin on 2007-05-25, 19:07:43 (67.172.255.89)
I have 8 power tubes in my amp to bias. This takes approximately 5 minutes . But the Audio Research VT 100 II takes longer. For a detailed explanation go to thetubestore.com and click 6550 Winged "C" .......
190: SLAM 100 schematic (4.81)
Posted by notout on 2005-02-12, 10:58:02 (63.249.67.120)
Having blown a tube listening to "One of These Days" (Pink Floyd) recently--even at a moderate volume--and consequently being forced to purchase a new matched quad of Svetlana KT88s, i am seriously co .......
191: Bass amp and a hi-fi amp (4.79)
Posted by steven oda on 2001-11-08, 17:57:58 (24.205.10.75)
Roly, Seen a few Ampeg SVT (7027A and 6550 driven) used as hi-fi amps. When Jess Oliver designed the thing he had "clean" in mind. Little did he know that a few more plate volts and under-biasing thos .......
192: RE: Nope.... (4.79)
Posted by xti16 on 2012-10-16, 17:18:54 (64.53.227.168)
WOW - 8 or 16 tubes per channel. I hope you guys own part of a power company or live in northern Alaska. I have an Octave V70SE and the heat from it is more than I imagined. Of course the sound makes .......
193: Re: 7591 replacements (4.78)
Posted by scholl on 1999-07-22, 07:43:59 (4.10.19.49)
The output tranny maybe 2-4k and most pentodes can work if you have enought heater current. The main problems are biasing and screen voltage. if the power supply powers more then the power amp tubes a .......
194: Re: tube biasing revisted (4.77)
Posted by steven oda on 2002-09-27, 15:47:52 (24.205.18.0)
DLaker, For FIXED BIASED amps (the ones with adjustable pots): Too hot or underbiased power tubes run hot, to the point of orange plates. Distort early. Clip early. Too cold or overbiased amp will sou .......
195: New to tubes - questions (4.77)
Posted by klaus on 2000-03-14, 00:02:14 (195.58.37.174)
well, after some research, but some things still unanswered and there's more to come! - Most commercial designs leave all tubes open, without screens; the old tube stuff I remember always had small-si .......
196: Biasing... (4.77)
Posted by steven oda on 2002-07-08, 22:49:51 (24.205.20.241)
HD, These are great sounding tubes---but I've found that they drift in bais, more than most other EL34 types. You really needto burn them in & re-bias them at the same time. A couple of amps I redid-- .......
197: You Might Be Right (4.75)
Posted by AbeCollins on 2006-02-26, 08:24:34 (67.176.116.152)
The best sounding tube amp in my system was the AES/Cary SixPacs which sound better all around vs the ARC VT50 which I'm playing with at the moment. The AES/Cary SixPacs use 6 EL34 tubes in triode mo .......
198: Re: Everything has a price (4.75)
Posted by Abe Collins on 2001-09-02, 15:03:00 (65.10.208.131)
Are AR power amps so sensitive to precise tube matching that its practically a requirement that AR customers buy replacement tubes direct from AR (at highly inflated prices)? I'm not trying to diss AR .......
199: JJ E34L & biasing (4.74)
Posted by steven oda on 2002-01-25, 13:42:38 (24.205.9.166)
These are good tubes. But, to get them to sing, you need to bias them a bit higher, than usual new EL34. For instance, I bias them at 40-45mA, if the plate voltage is 400 VDC. The JJ EL34 would be bia .......
200: RE: There is a difference between "self Biasing" and a robot. (4.74)
Posted by DAK on 2015-06-06, 12:22:20 (66.91.170.242)
"Reality, I don't know, and simply place my trust in what I've been told by the distributor. I would think he has a reputation to uphold. And based on my dealings including warranty concerns, no issue .......
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