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Blown power tube: what now?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Breezecookie, May 30, 2014.

  1. Breezecookie

    Breezecookie Tele-Meister

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    So I powered up my PRRI a few minutes ago to check things before tonight's gig. I got weird thundering and sputtering. I looked in back, and one of my power tubes was doing some cool purple arcing and flashing, much like in this video:


    So I replaced it with a spare EV I had sitting around, and all seems to be well. Full disclosure: the amp is only a few months old, but I did accidentally leave it on all night (volume only at 2) earlier this week.

    So my questions:
    1. Is it good for tonight?
    2. Is there a bias thing I need to do eventually?
    3. Should I just replace both?
    4. Is there a way to buy them pre-biased/matched?
    5. What's a good power tube upgrade I can do (if I need to be replacing them anyway)?

    Thanks muchos!
     
  2. muchxs

    muchxs Doctor of Teleocity

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    It's not widely publicized but the supply voltage in a PRRI is 440v. That makes it a torture chamber for reissue 6V6s.

    There is always some guy who says,

    "I've had my PRRI for (pick a number) and I haven't had any problems.

    He must be one of the lucky ones.


    Probably.

    Probably.

    Probably.

    If you replace both you should check bias. These amps are shipped biased cold to make the tubes last longer. They sound better biased hot but... well, you know.

    Yes. Buy a matched "quartet" of 6V6s. That's a matched set of four. That means if you pull a pair out of the set and bias for that pair bias should be correct for the leftovers which become your spare pair. You should in theory be able to replace them one at a time using spares from a quartet.

    They sell for around $20 per tube or $80 for the quartet.

    JJ sells a mutant 6V6 that survives high voltage better than most 6V6s.

    You're welcome.
     
  3. Breezecookie

    Breezecookie Tele-Meister

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    Thanks super muchos. I'm always looking for an excuse to "upgrade" something. I might try to take on the bias myself, or I might take it to a tech (they're few and far-between here in the sticks, but I think my luthier could probably do it).

    I had no idea about the power supply. That *IS* a well-kept secret.
     
  4. muchxs

    muchxs Doctor of Teleocity

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    I generally don't discuss bias because:

    A) You need to measure high voltage in a live amp to bias it correctly. Many tech discussions start with,

    "Tube amps contain high voltage! Be careful!"

    You usually still need to poke around in live high voltage to set bias. :rolleyes:


    and

    B) If you set bias too hot you can damage your amp. Too cold generally sounds like poo. Having said that it's not something you set by ear.

    The solution is a Bias Rite type meter. It comes with a couple octal plugs and a couple meters. Plug it in, hit the numbers... good to go!


    I'm Old School so I poke around in live high voltage.
     
  5. BiggerJohn

    BiggerJohn Friend of Leo's

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    Woah, EL34s in a Princeton? WTH?
     
  6. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    The video wasn't his amp. ;)
     
  7. Breezecookie

    Breezecookie Tele-Meister

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    Sorry- yeah, the video was someone else's- I was just showing what my tube had looked like as it was freaking out.

    Gig went fine this evening. I ordered matched JJs that should get here this week. My luthier ws at the show, and he says his amp guy will be coming through soon and will be able to do the biasing. So we're happy all over.

    Thanks again, folks-
     
  8. Berndizzle440

    Berndizzle440 Tele-Holic

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    reply deleted... shoulda read a lil farther to see that was someone elses amp lol
     
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