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1974 FENDER TWIN REVERB HAS NRE TUBES NEW FILTER CAPS AND WAS REPAIRED BY RETIRED AUTHORIZED FENDER TECH. PROBLEM AMP HAS VETY LOW OUTPUT UNTIL YOU CRANK IT TO 8-10 THEN IT SOUNDS HORRIBLE DISTORTED AND LOW NOTES LACK DEFINITION (MUD) WHEN I PLAY AMP AT 5-6 ON MASTER AND PREAMP KNOBS IT HAS HARDLY ANY OUTPUT, PLUS TURN THE GUITAR VOLUME DOWN AND IT SOUNDS LIKE A TRANSISTOR RADIO FROM 1960. HELP TECH SAYS EVERYTHING IS OK ONE OF US IS CRAZY.

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Check the speakers try to connect another speaker.then check the output transformer and the resistances at the bottom of the 6L6 tubes.then check the bases of output tubes and the output tubes matching trimmer if your amp have it.then check change the volume pot.then check the ceramic capacitor i n the input of the last 12ax7 tube in the power amp input.

Posted on Jun 13, 2010

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Hello Ktabbott,
I am going to ask you to do a strange thing, that is check the volume pot (potentiometer), make sure it is an audio taper control and not a linear taper control. This is a common mistake, linear taper pots being used instead of audio taper pots. This is what your problem sounds like.
Thank you,
Shuttle83

Posted on Jul 22, 2008

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This sounds like a power supply problem. The high voltage for the tubes is not right. Either you are missing an amplification stage because this or one of the coupling caps is faulty. I'd have to see the unit itself to give you any more details.

Dan

Posted on Jul 22, 2008

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Here is the schematic:

http://elektrotanya.com/fender_vibrolux_6g11_schem.pdf/download.html

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1 Answer

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I have a Fender tube amp The Twinn. 4 6l6 2 12at7 and 4 12ax7. Mu reverb is dead and I here some strange oscillation. I suspect the 12at7 in reverb and one 12ax7 Both microphonic and very dem fil. ...


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Yes, they could be causing the problem.The filaments are a little hard to see sometimes, you will always get a little microphonic activity about preamp tubes. It may also have failing capacitors depending on how old it is. Is it a "Twin Reverb". Let me know the exact model and we can be a little more specific of the problem and solution. Cheers


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