No NFB with a cathode bypass cap would be an interesting option to have, since it’s the configuration that would give the most gain.
NFB vs no NFB makes a difference but I’m not sure the two options for the NFB location would be very audible.
I would go with a simple switch that disconnects the NFB.
That’s actually how I had it set up before the PT failed. It would certainly be easier to wire that way.
Fortunately these components can all be mounted to the switch so I’ll have an experiment around when its together and see what works best. Doing it this way has the added advantage of being able to totally forget about the NFB loop until the rest of the amp is working correctly without worrying if the -ve feedback is actually +ve.
The parts were dispatched from Tube-Town today so I should be able to make a start soon.
I’ll be folding the chassis in work tomorrow when no one is looking!
Ive found/rescued a nice sized piece of ally that should be just the job!