[aferguson]

Thanks Edward and Terry for the valuable info. I love an underdog and I'd love to see these up and running again!

As I work on these I have decided to do some temporary modifications to evaluate performance. I'm afraid I'm not wedded to the idea that all amps should stay in their absolutely original state (warts and all). I've been corresponding with Claus Byrith about the amp, following on from my interest in his mods to the Mullard 5-20. I was keen to try running the EF86 in triode mode, and Claus has kindly looked over my plans and made some helpful suggestions. I plan to implement these and see what the results are like, given that I have another original still sitting untouched, and can always go back to "plan A" if things don't work out.

The rough schematic for the modded version is attached. You will see a temporary cathode resistor and pot on the EF86 to establish the value required to reach Claus's recommended anode voltage of around 70-75V.

You will also notice some component removals, and several value changes.

I will need to do the work and then put this on the scope to see how the feedback resistor/capacitor values are behaving with the output transformer. I haven't gone beyond square wave examination before so if I end up in Bode plot land it could be Christmas before I struggle out!!!!!

Lots of tweaking required but I'll let you know how things go when I can.

Best wishes

Andrew