How long can I expect the el84 powertubes to last?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by HeeHaw, May 10, 2005.


  1. HeeHaw

    HeeHaw Member

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    I'm getting to order an el84 amp and was just curious more than anything else. The amp is a 36 watter based on the 18 watt Marshall thing. I usually play several hours a night and gig once a month with church gigs in between.
     
  2. RussB

    RussB low rent hobbyist Silver Supporting Member

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    A lot depends on the particular circuit...for instance, my Mesa Studio 22+ runs the tubes at 120%...tubes (JJ's) last around 6 months or so with sporadic playing. Back in the early 90's when I was playing a lot with this amp, I would swap the nice Phillips 6BQ5's out every 3 or 4 months...and they were cooked!

    A Vox AC30 is hard on tubes as well. I don't know about that Reinhardt
     
  3. Blue Strat

    Blue Strat Member

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    What Russ said. In most cathode biased (aka "self biasing") EL84 amps, the EL84s are run well beyond their design maximum which leads to short tube life. Why the amp designers don't run them cooler is beyond me. A simple fix for this situation is to install larger value cathode resistors.

    If the amp is "fixed bias" (which means that the tubes require biasing), life expectancy will be inversely proportional to how hot you set the bias.
     
  4. goneracin

    goneracin Member

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    I run mine a touch cooler than the traditional circuit does. I have amps that have been used pretty regularly that have used the same set of power tubes for well over a year. I know marshall ran the tubes pretty hot, but in the interest of tube life, i tamed it down a bit, without totally changing the character of the amp.
    I think with your amount of playing time, even using current tubes you will get a decent life outta them.
    If you go to big on the cathode resistor, it changes the overall response and flavor of the amp, just as changing the bias does in a fixed bias amp. Some may like the change, and some may not, and are willing to have a little shorter tube life in exchange for that tone they want.
    Bob
     
  5. Blue Strat

    Blue Strat Member

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    True. The Vox guys finally did something smart in their new AC30. They added a switch ($3?) to allow the user to decide how the bias should be set.
     
  6. HeeHaw

    HeeHaw Member

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    :cool:
     
  7. HeeHaw

    HeeHaw Member

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    Thanks guys, I'm not really worried, I'm just curious. Hell, EL84's aren't that expensive in the first place. I'll just carry an extra quad of EL84's and a rectifier tube with me to gigs in case of failure.

    I did the same with my 100 watter.:)
     

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