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Post subject: Twin Reverb - volume won't go to zero
Posted: Tue Jun 26, 2012 6:03 pm
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OK, heres' the background. I aquired an early 70's Twin Reverb, master volume. I'm the second owner, only basic and poorly done maintenance done by previous owners amp tech. First - I freshened the amp up - new filter caps, new reverb tank and cables, new tubes, etc. It was working well, but I wanted to mod it back to an older config. I modded the amp back to AB763 using schematics (no more master volume), mod went very well, amp sounds great BUT, volume, when set to 1, still has some low volume on both channels. Originally was only on Vibrato channel, now it's on both. Not a major issue, does not impact higher volume playing, but it bothers me. Looking at schematic, don't see where the leak may be coming from. I have tried changing tubes out, no change. Have tried disconnecting reveb tank, no change. Do I have a bad cap somewhere? FYI - I'm pretty capable at tube electronics, have done many Fender 60's and 70's ampo restorations and mods, mainly to correct bias circuit shortcomings. Any info would be appreciated. Thanks, Dan.


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Post subject: Re: Twin Reverb - volume won't go to zero
Posted: Tue Jun 26, 2012 7:41 pm
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Possibly the volume pots still have some small resistance to ground when turned down. And/or, the ground circuit was interrupted when the wires were removed from the master vol switch. :idea:

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Post subject: Re: Twin Reverb - volume won't go to zero
Posted: Tue Jun 26, 2012 7:53 pm
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What's strange is that immediately following the AB763 mod everything was cool, then the Vibrato channel showed the not going to zero, then, a few days later, it was on both channels. It wasn't there when the mods were completed, played for a couple hours after the work was done. I first thoght maybe a bad (Vib channel) pot, but now that it;s on both, not likely. I will check the grounds on the pots...


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Post subject: Re: Twin Reverb - volume won't go to zero
Posted: Tue Jun 26, 2012 8:12 pm
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Maybe you tweaked the pots after the mod, and you probably didn't immediately try it turned all of the way down at first, then the problem became apparent?

Easy enough to check the resistance between the wiper and the ground side of the vol pots, with volumes all the way down, while you are at it.

And really, it's a TR, so why would you try to play your guitar with no sound from the amp anyway? :lol: Turn the guitar volume down and no guitar sound will come from the amp. :wink:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Twin Reverb - volume won't go to zero
Posted: Tue Jun 26, 2012 9:39 pm
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I agree with Shimmy. You have a squirrely volume pot. Again, try the old CAIG Deoxit Fader Lube, first (I say "again" as I posted this just yesterday, for another pot issue--- nothing personal) :D .

Be sure to use a contact cleaner FOR POTENTIOMETERS. As regular cleaners can dry out and ruin carbon contacts and lubricants in pots.

http://www.guitarcenter.com/CAIG-DeoxIT ... 1134931.gc

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