Rectifier Tube Question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by khudson, Feb 23, 2005.

  1. khudson

    khudson Member

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    The rectifier tube (JJ GZ34 S) went faulty in my Germino Masonette. I picked up a 5AR4 Groove Tubes replacement, but now the amp sounds different to me - I thought these tubes just change AC current to DC. Are my ears playing tricks on me or can there really be a change in tone and breakup? Are rectifier tubes rated and tested like pre-amp & output tubes? Thanks...
     
  2. Reeek

    Reeek Member

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    I can tell you that changing out a rectifier tube in a fixed BIAS amp technically requires a rebias so I would expect the tone to be affected in some way or another when changing rectifier tubes, even of the same type and mfg.
     
  3. khudson

    khudson Member

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    REEEK, thanks for you input. Your reply made me have to know more so I called Greg Germino. Cheers... By the way, here is his response:

    If you use the same rectifier tube, rebaising is not totally necessary in this case. But different brands of the same tube (in this instance JJ & GT) can have different effects on the overall tone. I am more likely to get closer to the original tone I had by replacing with the same make/model tube. (Sounds quite obvious now).

    So I orderd a JJ GZ34 from Eurotubes. The chinese Groove tube did not necessarily sound bad, but it changed some characteristics that I liked with the JJ and can tell that they were missing.
     
  4. Blue Strat

    Blue Strat Member

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    Yeah, they just convert AC to DC but in doing so they add varying amounts of resistance and capacitance. Series resistance affects sag which leads to differing amp response, pick attack, sustain etc. Different rectifiers may produce different DC voltages which affect headroom, high frequencies, bass tightness etc.

    A customer recently had his amp worked on by a tech who told him there was something wrong with the NOS rectifier I had sold him ("there must be something wrong with it, look at that silver stuff on the inside of the glass!").

    My customer played the amp with the JJ 5AR4 his amp tech had put in and then with the NOS Valvo I had sold him. My customer said that the volume increased by 20% (seems a bit much to me, but that's what he said). The amp tech was awestruck and he put the JJ rectifier back in it's box.

    But yes, rectifiers do only convert AC to DC:cool:
     
  5. khudson

    khudson Member

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    Mike, thanks for your reply. I e-mailed you directly for any possible specific info or additional thoughts/recommendations.

    I guess I still have a question as to can rectifier tubes be measured and rated like the other tubes so we know possibly what characteristics to expect from them?

    This Groove Tubes rectifier tube seems to give my amp more headroom (believe it or not)- It doesn't want to break up as early as it use to. I liked it the way it was for my particular needs. The bass does seem a little tighter however. I sure as heck don't need the Masonette louder though! (ha ha).

    Anyone?
     
  6. Reeek

    Reeek Member

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    Hi, Mike :) Rick Richardson from Reno, NV and a happy customer of yours.

    I guess the difference between that person in your story and me is that Valvo would have never been taken out for a JJ unless it was bad and the JJ was all I had. Not dissing JJ but I KNOW the tone from some decades proven tubes are more in line with my taste.
     
  7. Blue Strat

    Blue Strat Member

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    Hey Rick! Good to see ya!:dude

    KHudson. It might be useful to know which Groove Tube 5AR4 you got...Sovtek/EH, Chinese, JJ....I think these are the only possibilities.

    It's possible that the 2 JJs in question were defective (you did have to ditch yours) or were way at the low end of "OK".

    A regular tube tester will show differences in output (DC) voltage which may be helpful.
     
  8. Reeek

    Reeek Member

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    That's a good point in this case. I've had on average, a 10% - 12% failure rate on my new production tube purchases in the past two years. Failure not meaning total malfunction but high microphonics on up to full shorts.
     
  9. Blue Strat

    Blue Strat Member

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    PS, it's possible that your "5AR4" was behaving more like a 5R4 or 5Y3, either of which would give you less headroom and more sag. You may want to look into one of these. NOS examples are under $20 each...no sense in tempting fate with new production "third world" tubes.
     
  10. Reeek

    Reeek Member

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    Exactly why my stash of vintage is more than 150 tubes of all kinds except EL34 ;)

    I'm not going to get into a NP versus vintgae flame war but I just know what I like. Nothing more, nothing less.

    It's just that now, I have a large abundance of 6V6's and only one amp that uses them . . . Oh well, they aren't losing value for sure :)
     

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