I'll swop tubes and I have another set, so I'll try these, too. But assuming it's still out after I've tried this what's the next step or two for finding the problem?
I should note that at first I thought it was the interconnect, since when I twisted it a little the sound came back, but then got crackly and for a few minutes was going in and out. I thought for sure it was these new right angle plugs I got. But then it stopped working, even without those plugs. Tubes still glowing.