I thank you very much for that tip!!! I have searched the web, and all the magazine articles I could find on Joseph Marshalls designs, but didnt pick that one up.
I have used Marshalls origional modification that uses two OA2 regulators, and if I still have problems I will look into the feedback mod you describe.
I also was wondering if modern components might also help? I have most of the components ( passives, anyway) in precision versions as they are so cheap and freely available today. For instance the balance pots I have obtained are all 3 watt wirewound ten turn units, and resistors are .5% tolerance 2 watt units, so initial balance should be easy. I have used different coloured 4mm test sockets on all the points where measurements are taken to perform balancing and I have in the back of my head an idea using different coloured test wires that plug in directly, a switch to select each function, and a handful of resistors all contained in a box, so that I can balance "anytime" so to speak. The pots all have 1/8" shafts or 3mm with a screwdriver slot. This also means I dont have to cart the monster around and remove covers to perform the work.
Yep !!!
its taken me half my lifetime, but I do try to work smarter these days. I have redrawn the circuit as well ( its actually to "fix" any errors, in my drawing, hence the pencil scribbles where I need move bits n pieces ) to make it easier to understand.
Joe