Short tube life in class A

Discussion in 'Amps and Cabs' started by aussie_gear_maestro, May 1, 2019.

  1. jcarpenter

    jcarpenter Supporting Member

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    No KT66 is good for 6L6 swap out in most cases. But for El34's you may be able to use a KT88 or 6550.

    The impression I have is that those larger tubes can take more abuse.
     
  2. jcarpenter

    jcarpenter Supporting Member

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    Perhaps the the 6CA7?
     
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  3. jcarpenter

    jcarpenter Supporting Member

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    Or just get a cheap quad of EL34's and change em twice a year when you change your clocks.
     
  4. Fuchsaudio

    Fuchsaudio Member

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    It might sound cliche, but this is the first time this issue has come up with this model. I make a point of trying to balance a conservative design against good sound.
     
  5. Laurence

    Laurence Silver Supporting Member

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    FA, is the EH EL34 one of your standard offered tubes?

    Aussie, how many times have you had to replace this power tube?

    Thanks, trying to gain some insight...
     
  6. HotBluePlates

    HotBluePlates Member

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    I hear ya! That's why I wondered how @aussie_gear_maestro determined the tubes were only lasting 6-8 months. I don't know if that means they went microphonic, suffered a short, heater burned open, glass lost vacuum, or the tube just "doesn't sound as good as before."

    I suspect most things that could go wrong would indicate a shortcoming in the tube itself, rather the circuit using the tube.
     
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  7. Fuchsaudio

    Fuchsaudio Member

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    The amp should not get 6550's or KT-88's. Lets get that out of the way now. Firstly the tube clip won't allow the base to fit, but more-so, the filament current is excessive for the power transformer.
     
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  8. Daytona57

    Daytona57 Member

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    OP stated, that he runs the amp 30-45 minutes per day. The tubes are just warming up, when shut down.

    My understanding, is that tubes last longer when they are on for long periods of time. Military tube equipment, was left continuously, running for years.

    I use a solid state amp for short practice times and run my tube amp for hours.

    YMMV
     
  9. GT100

    GT100 Member

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    With good tone? Sure tubes can last for much longer but running true Class A typically is hard on tubes. As by the nature of Class A you are pushing the tubes hard even with the volume low.

    Lloyd
     
  10. No457 Snowy

    No457 Snowy Member

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    As I mentioned in my previous post I've had mine in for 5 years, not the same amp as the OP but still a Class A Single ended amp and regularly swap in a spare tube just as a checkpoint, (the other tube from a matched pair of 6L6GC) and I haven't found as yet any drop off in tone in my amp so I just put the original back in until then. Don't see any reason to change it yet after using it for 5 years. I have a feeling a lot of tubes get changed needlessly.
     
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  11. halcyon

    halcyon Member

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    Contributing a data point here: I've been averaging about a year from the 2x 6V6s in my Milkman One Watt Plus (parallel class A) before they start doing weird things (volume drop, buzzy decay on certain notes, etc.). That seems not unreasonable to me. And because of that, I don't use expensive NOS power tubes in this amp; just a matched pair new-production Tung-Sols. They sound great! I guess it'd be nice if they lasted a bit longer, but <shrug>... it's a class A tube amp and it owns.

    I usually get about 2-3 years from the 2x 6V6s in my PRRI, but that's a push/pull class A/B amp.

    Finally, my Victoria 518 (1x 6V6, class A) came stock with a new-production Tung-Sol. When that tube dies (it sounds fantastic), I'm going to try a NOS RCA Blackplate and see how long it lasts. Hopefully more than a week or so. :)
     
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  12. GT100

    GT100 Member

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    Are those NOS 6L6GC?
    Also what are the exact electrical conditions in this amp?
    Cause as most have said guitar amps running in true Class A eat tubes.
    My Guytron eats a set of EL84s up in well less than 1yr. Sure they will function longer but they loose their tone much earlier.
    With the Guytron I can run them colder (Class A/B) but the tone isn’t the same.

    Lloyd
     
  13. No457 Snowy

    No457 Snowy Member

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    The tube is a JJ 6L6GC. I checked the dissipation and it is running at 29.4W (just under the published 30W max spec for the JJ tube). The amp is a Trinity Tramp and it sounds great, I'm just adding this as a data point to illustrate that not all Single Ended Class A amps need to eat tubes.
     
  14. GT100

    GT100 Member

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    No, but there is a reason a lot of true Class A amps run the tubes hard.

    Lloyd
     
  15. HotBluePlates

    HotBluePlates Member

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    "Good tone" is subjective. But yes, in the situations I've tried them new production tubes have been plenty good-sounding compared to old production tubes, and for many years.

    I usually use old-production tubes though, "just because" I want to. And I've got a plenty-big stash of them, so that's what I do.

    I disagree with your characterization, as I noted here already. Quiet Class AB playing is easier on tubes than Class A, but loud Class AB playing is harder on the tubes.

    Either way, I haven't swapped output tubes in my tweed Deluxe or Super clones since ~ 2007, though both have gotten less playing time over the last couple years as I've acquired other amps. That's a mix of Class A & Class AB, and both new & old production tubes have been used in both amps.

    Every preamp tube in very likely every amp you've ever played is running Class A, and other than noise/hum/microphonics most are hard-pressed to find any reason to change aside from tone changes when tube rolling.

    The "reason" is power output: the nature of Class A is that if you idle the tubes at a lower dissipation, you get less clean output power from them, all else equal.

    I haven't had the "weird things" @halcyon experienced, and have had results like @No457 Snowy where tubes just keep going & going. Whenever I've swapped output tubes, at most I've noticed a bit more output power or a bigger, bolder sound from the new tubes.

    So outside of things that might be chalked up to shortcomings of individual tube samples, I struggle to understand how some determine their output tubes need replacing (which includes the OP who hasn't been back on the forum to share his rationale).
     
    Last edited: May 3, 2019
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  16. classicplayer

    classicplayer Member

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    How about class A amps that run in A/B mode (which is a push-pull mode), would EL84's tend
    to deteriorate more quickly? I had a Blues Jr. years ago (1st edition) that ran as A/B and was powered by a pair of EL84 tubes. My current Dark Terror is class A running as A/B.....I’ve been told.


    classicplayer
     
  17. GT100

    GT100 Member

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    Class A amps don’t “run in A/B mode”.
    Class A/B amps run in Class A/B and Class A amps run in Class A.

    Lloyd
     
  18. aussie_gear_maestro

    aussie_gear_maestro Member

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    Absolutely thanks for that. I'm putting it down to bad quality tube manufacturing because tubes used to last longer . Can you suggest a tube that's reliable and with all the sonic goodness .
     
  19. aussie_gear_maestro

    aussie_gear_maestro Member

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    I'm not to sure if everyone here has heard Fuchs take on a class A design but I was really blown away I didn't know the cleans so amazing in these amps i thought it was all about the harmonics in the distortion. Those classic clean/broken up on edge marshall and vox tones are just singing out
     
  20. aussie_gear_maestro

    aussie_gear_maestro Member

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    I'd really like to solve this post by picking everyone's brains on a good quality and reliable el34 , currently using EHX .
     

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