For what it's worth this is the schematic section of the reverb. The green overlay is the dry signal going to the reverb tank. The red overlay is the wet reverb signal after the tank.
Any chance you have a stereo, mixer, etc. with RCA ins? If you do and you can find an RCA to RCA cable, plug one end into where the white plug would go on the amps chassis and the other end into the stereo, mixer or whatever you might have that can be used to monitor a signal. The signal out of that jack is fairly hot, so keep the volume down on what you're monitoring with. If you get signal at that jack, it's a pretty fair guess the reverb tank has an issue.