Keith G wrote:

The Bad - It's humming like a good 'un and I suspect it's going to be a
bugger to sort....

Well, I'd expect it to hum.

A single-ended design doesn't have the inherent 'hum rejection' of the push-pull
output stage configuration.

Also, triodes have fairly mediocre anode impedances which make them more prone
to supply ripple effects than tetrodes / pentodes.

I'd suggest an extra stage of LC smoothing on the HT.


Graham