My Ampeg V4 Drops Volume!

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My Ampeg V4 Drops Volume!

Postby ChuckFalcon on Mon Jun 08, 2015 5:47 am

Hi everyone, I have a (mostly) fantastic sounding Ampeg V4 from the early 70's. I have been doing work on it for a month but it still has a problem that I can't figure out how to fix. On channel 2, the initial attack of the note will kill the volume. You will hear the note for a split second and then it will cut drastically, and sound barely audible. When it goes to "quiet mode" you can tap the chassis face plate and it will fix it, or jiggle the board that all the knobs are soldered to and and it will fix the problem, but as soon as you play another note, it will go back into quiet mode. Also, if you turn the amp into standby mode and then back into play mode, that will usually send it back into quiet mode.

Here is what I have done so far:

-Replaced all electrolytic caps
-Replaced tube sockets
-Tested all the tubes, they test good

I have been getting some good help from another forum, and it has taken me a long way but me and everyone else really can't figure out what the problem may be. Does anyone have any suggestions? I could really use the help.
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Joined: Fri May 15, 2015 6:47 pm

Re: My Ampeg V4 Drops Volume!

Postby PeterS on Thu Jun 25, 2015 8:02 pm

Sounds like bias of some stage is going wrong. If you can probe the cathode voltage of each stage in turn as you make the symptoms happen you can narrow down. Might be a broken circuit board trace?
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Location: Canada

Re: My Ampeg V4 Drops Volume!

Postby stratele52 on Thu Aug 06, 2015 1:11 pm

More answer in amps forum .

Bad solder , broken printed circuit .......
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Location: Québec province, Canada

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