Experience with JJ GZ34?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by tonemnstr, Jun 24, 2008.

  1. tonemnstr

    tonemnstr Member

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    I'm redoing a 65 Pro Reverb, new caps, new tubes etc..

    After replacing all the electrolytics I installed the new tubes & checked the bias then grabbed a guitar for a little test drive. The amp sounded as I expected, nice & clean, classic Fender..

    After about 15-20 minutes the fuse blew, upon replacing it I noticed arcing in the GZ34 when coming off standby. Tested the power tubes, OK. Tested the rectifier BAD.

    Anyone have any experience with JJs, good/bad etc?

    I'd sure like to think I can get more than 20 minutes out of a tube....
     
  2. Trout

    Trout Member

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    My experience,

    There apparently was a bad batch going around at one time. I bought 6 JJ GZ34's all had dead shorts internally. I needless to say was not very happy.

    Just last week I started using one from a recent purchase. No problems so far but only about 3 hours on the tube so it is to soon to tell.

    Arcing in rectifier tubes can eat up any rectifier tube quickly. Often it happens when either a bad cap or over capacitance is present.

    ALSO,

    Many transformers also have a tendency to generate arcs when going in and out of standby mode. Fender added a pair of diodes to protect the rectifier from this problem in the Tweed Deluxe re-issue.

    Some glitch capturing with a storage scope revealed some serious transients generated form the collapsing magnetic field in the power transformer. It is usually transformer dependent, and spikes of over 3KV have been seen on some transformers. The use of avalanche rated diodes allow most of the transient to be dissipated before becoming a lightning bolt inside the rectifier tube.



    [​IMG]
     
  3. teleamp

    teleamp Senior Member

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    I have had better luck with the JJGZ34 than other new production GZ34's. The best value, while the buy in is high, is a NOS, ANOS, or good used Mullard or similar. the payoff is the longevity.

    The problem with new production is that (other than a short lifespan verses a well made older tube) the consumer is the quality control.
     
  4. teleamp

    teleamp Senior Member

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    +1, I have started doing this also.
     
  5. Tallhorses

    Tallhorses Member

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    I've had terrible luck with rectifiers in general especially JJ GZ34's. I've been told they're the best new production rec tube. The guys at Carr told me they stick with Sovteks because the pins seem to be larger or inconsistent on the JJ's. I started using NOS with somewhat better luck. Price is really sky rocketing on NOS GZ34's... and to be honest I ordered 3 and 1 was bad so go figure.
     
  6. Blue Strat

    Blue Strat Member

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    Experience with JJ GZ34?

    Best of the new production GZ34s by far. Nothing is immune to failure.
     
  7. fiddler

    fiddler Guest

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    I had a JJGZ34 "lose vacuum".....Vendor sent a replacemnt....Put it in..........been working fine for the last 8 months

    Like Blue Strat says, no tubes (New production OR NOS) are 100% immune to failure...way too many variables thrown into the equation to expect a zero failure rate
     
  8. Rosewood

    Rosewood Member

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    I had a few bad ones about 2 years ago but all have been good lately.
     
  9. rcboals

    rcboals Supporting Member

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    #1 on getting a NOS in my 66 pro-reverb I got a NOS Telefunken for $70.00 Mullard would be good also. Haven't heard anything bad on the JJ's my pro reverb came with a JJGZ34 and it seemed to work fine, but I couldn't pass up the Telefunken. You might call Bob at Eurotubes and get his input. http://eurotubes.com/
     
  10. teleamp

    teleamp Senior Member

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    I very seriously think that Bob will say anything negative about JJ tubes...they're his livelyhood. And besides, the Russian mafia would off him if he did.
     
  11. rooster

    rooster Member

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    JJ's aren't russian.

    rooster.
     
  12. teleamp

    teleamp Senior Member

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    But the Russian Mafia is..... My bad.
     
  13. tonemnstr

    tonemnstr Member

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    Thanks everyone, some good insights..

    I went back and double checked the caps, wiring etc. and everything looks good so I'll have to wait on the replacement tube to show.

    Who carries the diodes mentioned above? That may be a nice insurance policy to add.
     
  14. teleamp

    teleamp Senior Member

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    Try a local electronics store if there is one nearby, otherwise www.tubesandmore.com or similar.
     
  15. slider313

    slider313 Silver Supporting Member

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    I've been using JJ GZ34's since they started production and never had a problem.I guess I've been lucky.
     
  16. jay42

    jay42 Member

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    I have two untested JJs in my box -- making me worry, plus, why would someone (Fender) choose an Avalanche diode. It has a 1500V reverse breakdown and is termed a "Fast soft-recovery controlled avalanche rectifier." Fast and soft-recovery sound warm and fuzzy, but an avalanche diode? Anyone?
     
  17. RedRock

    RedRock Member

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    I have had very good luck with the Sovtek 5AR4, which is the equivalent
    of the GZ34.
     
  18. Trout

    Trout Member

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    Putting these diodes on the rectifier is not a new idea, it has been around for decades in high end HiFi where excessive filter capacitance is present.

    I just thought I would mention I have been using UF4007 in this same topology and it is very effective at preventing arc-over in the 5AR4,5Y3, 5U4 and other rectifiers with close cathode to plate spacing. I have not had a single rectifier tube failure due to arc over since I started doing this.

    Special diodes don't seem to be required for this purpose. I have not had a problem with anything rated at least 1KPIV or above. (1N4007/UF4007, any of the types are ok also)

    Generally it is not an issue in all amps with standby switches but some power transformers tend to exhibit this issue. It also helps protect against hot power cycling and other oddities like sag/surge/dropout on the mains.

    It is actually very easy to install the diodes right on the rectifier socket and really, for the .95cents it is as good as screen resistors for insurance sake.

    [​IMG]
     
  19. Blue Strat

    Blue Strat Member

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    Unless you're willing to step up to NOS JJs are your best shot.
     
  20. TungstenAmp

    TungstenAmp Gold Supporting Member

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    I've switched over to the Weber WZ34 Copper Cap over the JJ GZ34/5AR4 due to the number of JJ's that have gone Tango Uniform.
     

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