Amp runs for 30 seconds, then fades out

[pine]

I have a 5E3 clone that has worked well for years, but now, I power it up, it plays for 30 seconds or so, then it gets fainter and fainter until there is no sound. I thought it might be a loose connection that was interrupting the circuit when it got hot enough, so I re-flowed every joint I could find, but of course the problem is still there. Now I'm thinking it is a component failure. Has anyone seen these symptoms before, or know what the problem might be?

[g1]

Are the tubes (heaters) still lit up after the sound has died?

[HBamps]

I am having a similar problem. I can play for a few minutes, then the volume fades out. It will come back after another minute or two, then fade out again. please let us know if you find the problem and how you fixed it.

[Ronsonic]

G-One asked the question.