Sorry to hear of your illness.
Yes - it could be a tube causing the reverb problem. V7 (one of the back tubes, far left looking at the back of the amp) is the reverb driver tube, a 12AT7.
V5 (one of the front tubes, 5th one in line counting from the guitar input side, a 12AX7) is the reverb recovery amp.
If you have some spare known-working tubes replacing those (I would do it one at a time starting with the driver) would be a good place to start.
One easy troubleshooting technique: if you hold your finger on the tip of the RCA plug that would normally be plugged into the "output" of the tank you should get a buzz/hum (like touching the end of a guitar cord) that varies in volume with the reverb control. If that works then the recovery circuit is working and the problem is likely in the driver side of things. Just for fun try it with the other cable to make sure you don't have an inadvertent swap of connections.
Not to be overlooked: possible bad replacement tank or cables. Not likely maybe, but it happens.