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Fender Twin 135 reverb squeel past 3-4

3/6/2006 10:34 PM
Fender Twin 135 reverb squeel past 3-4
I have a monster clean machine on the bench  
it has a weird problem it feeds back like crazy if you turn the reverb up past say 3 or 4  
I have been troubleshooting it for a bit  
just curious if someone may have run into this before,  
3/7/2006 3:34 AM
Don Symes

I haven't, but my first suspect is the reverb cables and/or tank. If you have a known-good set to swap in, that would be a good step to take.  
Have you worked your way through the reverb debug stuff in R.G.'s Tube Amp Debug Guide?  
3/7/2006 1:26 PM
Mark Burness
Have you got the tube shields on V3 & V4? Twins & SR are usually OK without them but as you're getting noise try it with them on.  
Sometimes using something to damp the reverb tank can help, like covering it with a towel/blanket.
3/7/2006 7:26 PM
Have had a similar problem. The cause was a bad ground connection with the reverb and tremolo jacks on the chassis.
3/7/2006 7:27 PM
Nico Verduin

Apologies for the anonymous.....
3/8/2006 4:16 AM

Thanks guys I had to put it aside for a bit  
but I will check it out soon again..  
I was trying all kinds of things like snubber caps  
its not ringing in the return amp or the mixer  
I am pretty sure its the reverb driver stage  
what a mess that master volume with the  
switch ick..
3/8/2006 1:16 PM

[QUOTE]what a mess that master volume with the  
switch ick..[/QUOTE]  
What a mess that whole amp is ! Theres just to much crap on that amp for the poor design work. I also agree that a ground problem is most likely the cause. Try ohming out the drive transformer as it shoud be around 1.2k on the blue and red wires and around 1.2 ohms on the green and red. However poor cables could cause a bad ground connection as well.  
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