Berning ZH270 help

If one of the tubes are not within it's spec, the amp will see it within 1/60 of a cycle and continue to try and correct it within every 1/60 of a cycle while limiting current to the tube, which turns the LED red, if you turn the amp off and then on again and the problem is gone for awhile, that could mean the tube warmed up and is now operating within it's specs.

So as Oneprof suggested, please swap the tubes from one channel to another and see what happens, I suggest only doing the outputs firsts and try it that way for a while and see what happens.
It would also help to know the age of the amp.

Please feel free to e-mail me.
Allan

Paolo, the noise you describe really is conducive to that of a tube problem, you need to take your time and switch one set at a time, and make sure you are changing them from one channel to another, as well, did you do any mods to the amp?
The ZH-270 is not a user friendly mod device by any means.

I hear stories from Europe of people cutting off the wrappers on caps and other stuff.

When you get the other set of tubes, we can go through the switching, so we can make sure it's in opposite channels.

Paolo.
Switch the input interconnects to the amp from left to right and right to left, see if the noise stays in the same channel.

The ZH-270 is different from the Siegfried, as is has different feedback settings, if you remove the pot, then you will have problems with sensitivity in low and maybe medium feedback, you will most likely hear pre-amp noise.

You might be able to do it if you are running a CD player direct but there are few pre-amps made, especially tubes ones that the ZH-270 will not pick up the noise without having to reduce the sensitivity of the input to the amp, the only other alternative is to find the exact resistance needed to which feedback you use and put a fixed resistor.