'68 twin reverb-reverb/tube questions!

I've got a '68 twin reverb that I love--it sounds awesome. But today I fired it up for the first time in a few weeks and the reverb doesn't work. The rest of the amp seems to be working fine and flipping the switch on the footpedal just makes a popping noise but doesn't turn on the reverb.

Now I've recently had new reverb tank put in and at that time I had the wires that make the connections into the back of the amp replaced. So is this probably just a tube problem? I tried switching around some of the tubes in there that were the same type (7025 for another 7025 a couple slots over) but that didn't help.

I've got no experience working on amps so I can't figure out what's probably a simple problem. And if it is a simple tube replacement, are there any magical tube layouts that you all have found to get the most from this amp? I've never really been disappointed by the sound, but if there is a way to get it sounding warmer and smoother that'd be great too. While I'm buying tubes, why not get this thing cooking, right? Thanks for your help!
matt

 

ok, thanks for the ideas. I turned it on with the reverb on 4 or so and shook the amp (not as easy as it sounds). It made the crashing noise as expected. I also fiddled with the connections (i didn't switch them b/c it was working before like this) and it still doesn't work. So does that mean that it's not a tube? do I have to drag it in to somebody who can open it up and look at it? Thanks again!