Fender Twin Reverb 135

[tube dude]

Hey Folks,
Anyone out there had any dealing with this Twin Reverb 135 w/master volume?
I have one that, with/without reverb tank when you turn up the reverb control..it just screams.
I have replaced the reverb transformer, changed V3-V4 tubes..still screams.
Without V4 there is no screaming but also no reverb...duh!
Anyone able to relate and suggest?
Thanks
tube dude

[Justin Thomas]

No need for it to be any different for any other amp, as they all used the basically same circuit... Did you open the amp up and check for loose wires? Bad grounds? Chopsticks? Voltages? I had a Princeton Reverb that did this, and it was a loose ground wire.

Schem link: http://vintageampguide.com/schematic..._135_schem.jpg
If anyone can put in a thumbnail, I won't mind...

Justin

[Jazz P Bass]

Does the Reverb footswitch work?
It should ground the grid pin of V4A.(Reverb Off)
Check that the grid does go to ground & continue testing that way.

Check the voltages of V4.
Plate: 250 Vdc
Flip your meter to read Volts ac & check the plate pin for unwanted ripple.
(which would indicate a bad decoupling cap)

Grid: 1.8 Vdc.

Check the voltages on the Reverb control.

If the .003 capacitor is leaking, you will get a Vdc reading on the control side of the cap. (not what you want to see)

[pdf64]

The cathode bypass cap of V4 (shared by both sections in cascade) may be bad.

[tube dude]

Twin reverb 135

The cathode bypass cap of V4 (shared by both sections in cascade) may be bad.

Thanks for taking the time. I found the problem. There is a 25ufX25v electro cap with a 820 ohm resistor from
pin 3 of V4A and then to the phono jack. The cap was bad!
Lesson learned for me.
Thanks again!
tube dude