Last summer I was battling my AMI "K" amp, and several folks here
were kind enough to offer me some help. The problem was a crackling
noise that appeared on power up, and I thought my output transformer
might be bad.

I ended up replacing the transformer, and the problem went away!
However, after using the amp for a couple of weeks, the noise
gradually returned -- except now it was a constant noise, whenever
the amp was on. Frustrated, I decided to just forget about the whole
thing for a while.

So... Yesterday I decided to dive into it again. I replaced the few
ceramic caps I hadn't replaced before, but that changed nothing.
I poked around with a scope, and was able to determine that the
noise started before the signal reached the second 12AU7 (V2).
I already knew the problem was in the power amp, because the noise
was present even with the pre-amp unplugged.

All arrows seemed to point to the resistors that attach to the first
12AU7 (V1) -- which I *thought* I had checked back when I re-capped
the amp. Nonetheless, I found that one of them was reading about 190K
instead of 100K. Maybe I missed it, or maybe its value drifted after
being used again for a while. I replaced it, and the other 100K resistors
on that tube as well.

And... the horrible noise is gone!

I learned a lesson: When repairing a tube amp, double-check those
resistors, and replace if there is any doubt about them.

Thanks again to those who offered advice on this.

-- Russel Willoughby