[joebog1]

I don't think the EL34 heater wiring passing close to the OPT will cause any hum, at least in my experience I haven't seen that. It could be a possibility though.

I usually run my feedback loops through good quality coax, after measuring the capacity of the length of cable required. I always run the feedback via the SHORTEST path possible and avoid ALL components from the input stage as far as is practical and all other components in general. Which brings me to another point !! 800 pF as correction capacitor on the feedback?? To me that sounds awfully BIG. I use an oscilloscope to choose the capacitor sizing/value while testing the amp with square waves. I choose a value that doesn't produce overshoot spikes, or rounding off, of the square wave.

You will never get this perfect however!! as any output transformer has its limitations. With my own transformers I get in the vicinity of 100 pF as the biggest value with smaller transformers. I start with a value of about 47 pF and select as testing proceeds.

Somewhere I have an excellent article from Radio Television and Hobbies magazine from the late 1950's that explains the technique in terms I can even understand. I will post it when I dig it up.

In the meantime enjoy the music.

Joe