OK, so the recovery works and the pan is OK.
The drive end has the problem. I will assume you have tested the cables. If not, do. The tube drives the transformer, so indeed, check the cathode voltage. Since ther is some voltage drop across the transformer primary, I will think the tube is conducting until you tell me different. If tehre is no cathode voltage, then the tube ain't doing its job.
Touching the plate makes a little pop and it reverbs some. OK, but now test the tube. Touch the grid. Now the tube should amplify whatever pop your meter represents. Check the grid for DC voltage. SHould be none, or maybe a very small negative amount. If so, that is good. Now touch your meter probe to the grid. REverb pop louder now? SHould. Flip your meter to ohms and touch it to the grid. Ground the black probe. Now your meter ohms test voltage will hit the grid. That should make a real solid pop through the reverb.
The amp works fine otherwise, right? That means the signal should be on the outer end of the 500pf cap. It should pass through the cap, losing some bottom end as it does, and feed the grid of the reverb drive tube. So sure, suspect that cap. This is a go or no go situation, so clip ANY little cap across the 500pf and see if the reverb wakes up. We don't care about tone, just does it work. If that wakes it, then replace the 500pf. Use whatever you have, not electrolytic, like .01uf, .047uf, .001, etc doesn't matter.
OK? We made sure the tube was conducting, tested the tube for amplification, and bypassed the input cap. That should find it.