JJ6v6S and the 70% bias rule

Discussion in 'Glowing Bottle Tube Amp Forum' started by misterdontmove, Mar 30, 2019.

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  1. misterdontmove

    misterdontmove Tele-Meister

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    So, I just purchased a pair of these and stuck them in my Ampeg Jet j-20. It's sort of a Brown Fender Deluxe clone with non-adjustable, fixed bias. It runs over 400 volts, and I previously cooked a pair of Tungsols in it. The JJ's sound GLORIOUS, but they're running 400 volts and 29ma, for just over 80% dissipation, according to Rob Robinette's bias calculator considering them to be 14w tubes (as indicated on the data sheets).

    All the research I've done seems to support that they'll function at this setting and again, they sound really good with no sign of red plating, even after 3 hours of play at full band levels. Some of the stuff I've found, including some torture testing by Lord Valve (I think), indicates that these things are nearly indestructible (I said nearly)! And, some of the stuff out there would suggest that they may be 17 or even 19 watt tubes (more akin to a 7591 or 6l6gb). Interestingly, Rob's calculator also has 15w to 19w listed under tube type. If I pick 17w the dissipation falls right on 70% dissipation.

    Anyone else using these tubes like this? Maybe we all should be! I will report back on longevity.
     
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  2. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I have used them all the time for years. My BFDR and BFD run at 460-465 volts! I used to bias at 22-25 ma and they were fine. Now I bias at closer to 15 ma. But I may move up a bit as I wasn't using a calculator specifically for JJ's like Rob's.
     
  3. D'tar

    D'tar Friend of Leo's

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    Keeps spares handy:) Glorious is hard to beat!
     
  4. viking

    viking Friend of Leo's

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    I believe I have seen several places that call them 18w tubes
     
  5. schmee

    schmee Doctor of Teleocity Silver Supporter

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    By the way, I modded my BFDR to 6L6's a year or two back. (basically a Vibrolux) The result was I found that JJ 6V6's sound nothing really like 6L6's. I think I understand people saying that though, but the difference is huge. The JJ's do have a tiny bit cleaner edge to them than normal 6V6's, but still smooth like most 6V6's compared to spanky clean 6L6's.
     
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  6. No457 Snowy

    No457 Snowy Tele-Meister

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    I agree as I've found the same to be true. I have a Trinity Tramp that allows swapping between 6V6 and 6L6GC, and the JJ 6V6 sounds markedly different to any 6L6GC I've compared it to in that amp. I think a lot of people just repeat what they read and I've noticed in any thread about the JJ 6V6 before long someone will come along and say "it's not a real 6V6" and I have no doubt most of these people are just repeating what they read and could not articulate as to why "it's not real 6V6".
     
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  7. Commodore 64

    Commodore 64 Friend of Leo's

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    Proof is in the pudding, I guess. I redplated a set of JJs at 90% cathode bias at 375V. If yours aren't redplating, then carry on!
     
  8. flyswatter

    flyswatter Friend of Leo's

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    I've used the JJs in a bunch of repairs where the dissipation was 14W or more and other tubes were red-plating. For example, I had a SF Champ in recently, single-ended that has a stock B+ value of 420 VDC. The Tung-sol in the amp was glowing red. A JJ 6V6S fixed the problem.
     
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  9. robrob

    robrob Poster Extraordinaire Ad Free Member

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    70% for fixed bias Class AB amps isn't a hard and fast rule. Merlin believes the max is really closer to 80% for normal tubes. With modern production tubes it's probably prudent to stick with 70% max with the exception being the JJ6V6S. it's a beast.
     
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  10. Henry Mars

    Henry Mars Tele-Afflicted

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    There is a tendency to try and coax more out of 6V6 and 6bq5 (EL84) tubes than maybe we should ...sooo they tend to run "hot" in guitar amps. If it sounds good and the tubes don't look like they are melting down you are probably ok. Just keep spare tubes around. I have amps with 6v6 and EL84 tubes ... I either carry spare tubes or spare amps with these guys.
     
  11. theprofessor

    theprofessor Poster Extraordinaire

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    Just keep rockin' 'em and keep some spares nearby. You won't likely need them. I'll bet the JJ's aren't even breaking a sweat. Smoke 'em if you got 'em!
     
  12. DADGAD

    DADGAD Friend of Leo's

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    I'm running a pair of JJ 6V6S tubes in my 70's Silverface Deluxe Reverb. They are idling at 25ma with a 5U4 rectifier. Cranked, the DR breaks up a lot like my 67 Bandmaster. I believe the JJ's sound more like a 6L6 than the RCA, KenRad and GE 6V6 tubes I have run in my DR.

    /2 cents
     
  13. misterdontmove

    misterdontmove Tele-Meister

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    That puts me close even if I consider the JJ6v6 to be 14 watts. Second consecutive 3 hour practice and they're not breaking a sweat! No sign of redplating in a dark room, and they sound great. Thanks for all the responses!
     
  14. misterdontmove

    misterdontmove Tele-Meister

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    I agree! I have a Super Reverb and the J20 response is similar at lower volumes. The JJs are a little rounder and clip a little softer but are very 6l6 like. I may even like them a little better.
     
  15. archetype

    archetype Fiend of Leo's Ad Free Member

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    Interesting. Thanks for the first-hand account.
     
  16. DrivinSouth

    DrivinSouth TDPRI Member

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    Every amp should be properly biased, and that even includes cathode-bias'd amps.

    Get to the root of the problem and bring the amp to a tech and have him install an adjustable bias so that the amp can be biased correctly.

    What you have right now is a wing-and-a-prayer that new tubes won't red-plate and blow.
     
  17. jhundt

    jhundt Doctor of Teleocity

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    "get to the root of the problem"? What was the problem again? He said the amp sounds 'glorious' with JJ 6V6's in it. 6V6's in and amp designed for 6V6's. With no adjustable bias, but they sound GLORIOUS!

    It sounds to me like there is no problem at all!

    The only problem may be that the OP is worrying too much about numbers on a graph, and not taking the time to play that glorious-sounding amp. It's not about numbers, it's about the sound. The numbers are there to help the designer; this amp was already designed a long time ago. And apparently it was well-designed. Why try to rethink all that?
     
  18. budglo

    budglo Tele-Meister Silver Supporter

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    I have the JJ 6v6S tubes in both my 68 Princeton Custom and my 65 DRRI . I biased them at around 70 percent and they really sound great.
     
  19. misterdontmove

    misterdontmove Tele-Meister

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    Oh its getting played! Almost daily at home volumes (LOUD) and 2x weekly at rehearsals at stage volume. The JJs are not even breaking a sweat. I really didn't get caught up in the numbers. My point is, after doing a lot of research, there is evidence to support that the JJs are capable of higher wattage. In almost every case you see the term "they are not a true 6v6" or they are more similar to a 6L6. In any case, if these tubes are actually 18 or 19 watt tubes, they're not running over 70%. Just wanted to pass along my thoughts and observations. They're still running strong, loud and sound "glorious"! I'll let you know if they blow!
     
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  20. jhundt

    jhundt Doctor of Teleocity

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    I should have said that "sometimes some people worry too much about numbers...".

    You are not the one who is worrying. Thanks for the information you have shared.
     
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