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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Can I substitute 5U4G for an amp that calls for a 5U4GB

Discussion in 'Glowing Bottle Tube Amp Forum' started by grolan1, Aug 30, 2017.

  1. I received an amp that calls for a 5U4GB and the tube was broken in transit. It's an 81 Fender Princeton Reverb. I happen to have a 5U4G that I plugged in and tried the amp and it sounds fantastic.

    Is it ok to use this tube or should I get a 5U4GB as soon as possible?
     

  2. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    A 5U4G is fine. Rock on.
     
    grolan1 likes this.

  3. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    To explain why it's OK - the "B" indicates a later version of the tube. It handles more current and input voltage. Theoretically it puts out a little more DC voltage but not enough to be significant. I've always used the more common 5U4GB's as replacements unless someone wants to pay for expensive NOS tubes. Plate voltage differences are essentially the sme as always seen with modern wall voltage.

    The only new 5U4's I recall are Chinese coke bottles, which I don't care for. from a physical durability standpoint.
     
    grolan1 likes this.

  4. Appreciate the help!
     

  5. alnicopu

    alnicopu Friend of Leo's

    Oct 3, 2009
    georgia
    Might I suggest a 5v4? My 76 princeton Reverb was hitting the plates at about 435+vdc. Stuck a 5v4 in it and took it down to almost dead on the schematic spec.
     
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  6. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Here is a link to a spec sheet for some of these rectifiers. Note that the 5V4 drops less voltage than any other rectifier other than the GZ34. Alnicopu's voltages should have increased when going from a 5u4 type, which is what the '76 Princeton/Princeton Reverb should have in it from the factory, too a 5V4. If alnicopu had a GZ 34 in that amp, then yes the 5V4 would drop more voltage. If there was a 5U4 in there and the 5V4 dropped more voltage than the 5U4, then I suspect that 5V4 is Not all that it should be...for one reason or another.
     
    slider313 likes this.

  7. alnicopu

    alnicopu Friend of Leo's

    Oct 3, 2009
    georgia
    I stand corrected. I did replace a gz34 with the 5v4. Not sure what i was thinking when i commented. It was the "mamma bear to goldilocks" rect. for my PR though.
     

  8. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Alnicopu, I figured that you had a GZ34 in that amp. Even if you had the 'proper' 5U4 in the amp, the voltage would probably be above that 410vdc on the schematic due to the higher wall voltage. There is one thing that, imho, Fender amps from the Sf schematic era do not need is a GZ34 in the amp. All of them went to 5U4's at some point starting in May, 1968. I have witnessed a '76 Vibroverb that had exact schematic voltages with a 5U4, though....when properly biased that is.
     

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