More likely, the problem is mechanical in nature. Check to see that the Molex plug that connects the tank and the chassis is making good contact, check the tank connections where the wires plug into the tank, and check the tank coil wires that connect the small transducer coils to the RCA jacks inside the tank itself. Any problems with these wires will cause the symptoms that you describe.
Additionally, there may be something loose on the circuit board in the reverb section. If you feel able, pull the chassis out of the amp and look for loose components on the board. The reverb tank wires will lead you to the area of the board that contains the reverb circuitry. Also. check the area around the reverb control for cold or broken solder connections.
Hope this helps.