Hard to tell until you get in there. But if the circuit is indentical to the V4 - which is what my memory serves (not enough time to consult a schemo now) the reverb is driven from a 6CG7 capacitively coupled. There is a large plate resistor then the cap and then another power resistor from the cap-reverb in junction to ground. Common culprits on these amps are the plate resistor, the coupling cap, and the resistor to ground - all three commonly fail but I've never determined which component started the cascade failure - but I've cured the symtom of "no reverb" in these circuits at least a 1/2 dozen times over the years by replacing the same three components - and occasionally the 6CG7. If you've got enough experience to repair this yourself you will be readily able to identify the parts I've noted. If not then perhaps seek an experienced tech.