Fender Silverface Pro Reverb-reverb problem

[Gareton]

Someone please help! I was given a ’79–’80 silverface Fender Pro Reverb amp serial# F916503. It’s seen better days but cosmetically it’s in great shape so I’m putting what little money and expertise I have into it. My main problem is in the reverb circuit. The tank was shot when I got it so I purchased a MOD unit from AmplifiedParts.com made for the Pro. (It’s not great but better than nothing) I was disappointed to find that the send circuit to the reverb was not working. I have output from the tank, but nothing coming out of the send to jack. I know it’s not the tank as I tried it in my Deluxe and it worked fine. Any suggestions?

[xtian]

Already tried replacing the reverb tube? Check voltages on the reverb transformer next.

[Milkmansound]

could be as simple as the wiring - Fender used some crap pre-made RCA wires in the 70's

try with known good cables or test the cables

[Gareton]

Thanks for the replies. I appreciate the help. Problem is, I'm not a true technician and don't know which tube IS the REVERB tube. It's not a cable problem though, I've been able to troubleshoot it to the jack that sends signal to the REVERB unit. (I took a known good RCA-to 1/4" cable, taking the REVERB OUT jack and feeding it to the NORMAL channel, sending a signal to the VIBRATO channel and turning up the REVERB knob... no signal out of the NORMAL channel! So if it's a tube, which tube could it be?

[Milkmansound]

Take it to a tech

[Randall]

Some basics. The reverb pot doesn't send to the tank, the tank is always getting signal from the Vibrato channel. See the small transformer among the pre-amp tubes on the right? That's the reverb transformer. The 12AT7 on it's right drives transformer which in turn drives the tank. After exiting the tank, the reverb signal is amplified again by the 12AX7 on the other side of the transfomer, goes through the reverb pot, and is mixed into the Vibrato channel.

It may be less confusing to use another amp or mixer or whatever to send your RCA to 1/4" cable to for signal verification. If you don't have a spare 12AT7, you can pull the first 12AX7 on the far right (that's the Normal channel pre) and try that.

If you get noise when shaking the amp or tank, then the reverb recovery tube is working. If you get no signal out of the reverb send RCA jack, then it's likely either the reverb drive 12AT7 tube, the reverb transformer, send cable or one of the few components in that part of the circuit.