twin reverb 100 watt

[timm1954]

I have an old 1973 Fender 100 Watt Twin reverb, it sounds clear and good, exept the Vibrato doesn't work. The speed control and intensity controls don't effect or change anything as far as the effects to the Vibrato go. I took the unit apart and inspected the wiring and circuits for obvious signs of damage, but all seems O.K.
All the tubes seem to be lit up O.K. I swapped the like tubes (12AT7's & 7025's) to see if that was a problem, but it didn't help. The foot switch doesn't turn the Vibrado on or off. The A - B ground switch didn't do any tricks either.It does turn off and on the Reverb. The foot switch is new. Tried with no foot switch plugged in also, no help.
Any ideals of what might be wrong with my unit?
Thanks.
Tim

 

[Trout]

I seem to recall a few threads on the same problem at a couple guitar amp sites I frequent. If memory serves, it was a capacitor issue in most cases. I forget the specifics.

I'll try to locate the info later this evening.

Trout

 

[m6tt]

it's the oscillator...I am sure you can find the schematic online, but I believe trout is right on. I would imagine recapping an re-resitoring the oscillator portion of the tube would bring it back right away. You could also make sure that the cable hasn't broken on your footswitch. I have also heard that sometimes the Light Dependent Resistor unit goes out of spec, unfortunately I have not heard the greatest things about replacements.

 

[Geek]

Hi, maybe this will help?

I found the schematics here: http://www.el34world.com/charts/Diagrams.htm

Cheers!