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Post subject: 1970's Fender Twin Reverb Silverface Hum/Noise Problem
Posted: Sat Jan 25, 2020 2:23 am
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I'm having the same problem as the previous post below from mydeadblues
Post subject: Help 1970's Fender Twin Reverb Silverface Hum/Noise ProblemPostPosted: Tue Oct 17, 2017 1:35 pm

Having read through the post it seems there was no resolution posted, just the discovery of a burnt filament adjustment pot. I could assume that was the issue, I suppose.

My Twin is the same model. The only difference is that the Master Volume circuit and wiring has been removed, as well as the filament hum pot and was replaced with (2) 100 ohm resistors at the pilot lamp.

Problem described as follows: With the power on and standby off and all controls zeroed the amp is quiet. Turning up any one of the tone controls on a given channel and the raising the volume a loud 120hz buzz occurs and gets louder as the volume is increased. This occurs on both channel whether a guitar is plugged in or not.

I've found that the buzz can be eliminated completely by touching with my finger either of the preamp stage's coupling caps. Touching any other caps has no effect on the buzz. The amp sounds great with a finger on one of the caps.

Solder points look as new throughout, including pots and jacks, tube sockets, etc. And board poked and probed thoroughly.
I've checked and rechecked all grounding connects. The amp has been completely recapped
Voltages are all to spec.

(I've been told a number of other techs were stumped by this problem, too). :?

Any help will be much appreciated.Image


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Post subject: Re: 1970's Fender Twin Reverb Silverface Hum/Noise Problem
Posted: Sun Jan 26, 2020 10:51 pm
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This does not sound like a parts failure if it occurs on both channels. The coupling caps are near the master volume circuit. Maybe you should go over that work and look for grounding problems or open circuits. Reinstall the MV if you can to see if it fixes it


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Post subject: Re: 1970's Fender Twin Reverb Silverface Hum/Noise Problem
Posted: Tue Jan 28, 2020 11:38 am
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Thanks, sounds reasonable. I'll give that a good look.


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