5U4GB rectifier tube

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by gkelm, Aug 23, 2004.


  1. gkelm

    gkelm Supporting Member

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    Hey Gang-
    My recently acquired '73 Pro Reverb came with a Weber Copper Cap SS. The amp sounds great as is, but you know...gotta tweak. I'd like to try a 5U4GB tube...considering an cheapie EH for $12.

    How much of a difference will I notice? Am I better off plunking a bit more green down for a better tube? Suggestions?

    BTW, my first Fender over 20 years...getting back to basics & diggin' the sparkle. :)

    Thanks.
    Greg
     
  2. Blue Strat

    Blue Strat Member

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    Contrary to popular opinion that rectifiers "are only in the power supply and can't make a tonal difference", I've had dozens of customers rave about the tonal improvement they've gotten from NOS (over Russian or Chinese) rectifiers.

    For $8 more than the EH you can get a US made NOS 5U4GB which will likely last 30+ years.
     
  3. hunter

    hunter Supporting Member

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    Not sure what a "SS" model Copper Cap is since Ted doesn't identify a SS model on his site. If you mean the amp has a 5U4 Cu Cap, the difference is gonna be real small. I have found variability in current/voltage characteristics for different mfg tubes. So for a spec'd 5U4, the voltage at a given current may vary from tube to tube. The voltage change may or may not be enough to hear.

    One other small detail. 5U4 tubes have larger spacing between plate and cathode relative to tubes like 5AR4s. The thought is this increased spacing makes the tube a little slow to respond to changing power supply needs. A few years back this wasn't thought to be the best thing but who knows what the buzz is now. Can I hear this "slow" response? Not really. At any rate the Cap doesn't have this slow response.

    If the "SS" Cap is a diode only version with no forward resistance (as in no voltage drop), the change to a rectifier with the voltage drop of a 5U4 would probably be audible since the 5U4 drops the power supply voltage. In this case, the amp will loosen up and get a little less aggressive with the 5U4.

    In either case (certainly in the latter) a rebias is recommended. Me? I use the caps. Inexpensive, reliable and functional.

    hunter
     
  4. gkelm

    gkelm Supporting Member

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    Thanks to all for the feedback.

    Hunter: it is the Coppper Cap you speak of (ss = solid state, not a different model). I borrowed tube from a buddy, and as you suggested, I did not hear a significant difference.

    Thanks.
    Greg
     
  5. hunter

    hunter Supporting Member

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    All Copper Caps are solid state. Some Caps have components added that make the solid state device behave more like a tube (forward resistance, inrush current limiting and the like). There is a Copper Cap that is designed to behave like a 5U4 (and one for all the other tube rectifier types). There is also a Copper Cap that is a diode without the voltage drop. Which kind of Copper Cap do you have?

    hunter
     
  6. gkelm

    gkelm Supporting Member

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    Yes, I realize they are all ss, that's why I was asking about the difference with a tube. :) Mine's the WU4GB, which appears to be Ted's replacement for the 5U4GB. So far sounds very close to the tube...but I'll play with it. THanks for the help.
    Greg
     

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