Input or output cable to the reverb pan not plugged in
Failing reverb drive tube
Failing reverb recovery tube
Bad reverb tank: measure the resistance between the center and outside conductors
on the RCA jack on the reverb tank. It should be less than 2K ohms for all types of
Hammond/Accutronics tanks, at both input and output sides. ManyFender amps may have a
resistance of only 2-4 ohms at the input side. This is normal. Other amps may have higher
input resistances, from several hundred ohms up to a couple of K. If the resistance is high,
the tank is bad. You can look inside the tank to see if one of the little wires have come loose
from the RCA jack; some tanks can be saved this way. If the little coils at the ends of the
springs are open, get a new tank. Sometimes the delay springs break. You're welcome to try
to solder/putty/glue them back together, but don't expect too much from this.
Very faint or thin reverb
This is caused by too little signal getting through the reverb path.Could be:
Failing drive or recovery tube
Failing component making one of these tubes be biased incorrectly.
Hum from reverb
Open ground/shield on reverb cable
Dirty/corroded RCA jack/plug on reverb cable
Broken ground wire inside reverb tank
Hiss from reverb
drive or recovery tube going noisy
Resistor going noisy in drive or recovery tube circuit
Distorted reverb sound; failing drive or recovery tube or failing component
making one of these tubes biased improperly
Crackling or popping sound from reverb
Squealing noise from the reverb, affected by the reverb control