Is this bad?

The amplifier was a recent AudiogoN classifieds purchase. The seller indicated that the bias was set just prior to packaging. The tubes are fairly new.

I'm thinking I'll rotate a tube from a different socket, and test it out just long enough to see if it follows the tube.

Apparently the amp needs to be biased by a technician. I could handle it with proper instructions.

Thanks for the info!

he had it modified for different tubes, replaced the caps and resistors, and updated the wiring. Aparently he had his tech that did the mods bias the amp prior to sale. So at worst I can get the info from him. The bias adjustments are supposedly not "user accessible" but I think I can handle it with clear enough instructions.

The tubes were removed, well labeled and shipped in a separate box. The amp was labeled as far as what tube went where.

I've been listening to it now for 3 hours straight, and the problem has not recurred.

No, the tubes were not labeled per socket. So the output tubes could be in any of 4 slots, and any of 2 for the input.

I'll contact the seller and get biasing instructions.

I've not had another episode of noise like the other night. I listened for 4 hours last night and it worked fine. So for now I'll make sure I'm around while I listen, and get it biased as soon as I have the instructions.

Thanks to everyone for your help.