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Post subject: Vintage Twin noisy pulsating vibrato/ footswitch pedal
Posted: Tue Aug 13, 2013 3:05 pm
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Hobbyist
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Joined: Tue Aug 13, 2013 2:02 pm
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Hello,
I am brand new to this forum (which is a great help).
I have vintage 1965 Twin. Just had it biased, serviced and all new tubes put in. I still have a LOUD pulsating even with nothing plugged in. Tried 3 old footswitches and a brand new one. Same issue. With the reverb set to zero it is faint. I need my reverb though.
Here's the kicker. If I put my hand near the cord or footswitch itself the sound goes away almost totally. VERY faint. ANY ideas would be very much appreciated.

JAK


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Post subject: Re: Vintage Twin noisy pulsating vibrato/ footswitch pedal
Posted: Tue Aug 13, 2013 3:32 pm
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Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
breakup, welcome to the Forum! :D

Have you tried different 12AT7 and 7025 (12AX7) in the reverb stage? That's V3 and V4--- reading right-to-left on the layout (bottom half of link).

If that doesn't help, sounds like you have a coupling issue. When was the last time your main power supply electrolytic caps were replaced?

Good luck! Keep us posted.



http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: Vintage Twin noisy pulsating vibrato/ footswitch pedal
Posted: Tue Aug 13, 2013 4:07 pm
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Joined: Wed Mar 31, 2010 12:48 am
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Check the 220KΩ resistor tying the reverb footswitch jack to ground. If the solder joint has lifted from the chassis or the resistor itself is bad, that might be the source of the oscillation.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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