[mike s]

I have a couple of output transformers with separate feedback windings, and was hoping that one might be a suitable replacement for the failed transformer in the RCA 82 C4 Monitor Amplifier. Schematic here http://www.waltzingbear.com/Schematics/RCA/BA-4C.htm

However it uses a high impedance winding (1/6th of primary anode-anode), whereas the transformers I have both use low impedance windings, about 1:100.. I have a schematic for a British circuit by P J Baxandall - last on this page http://mike.wepoco.com/Home/retro-ge...rld-amplifiers which places the feedback winding in series with the input pentode cathode, rather than the high impedance potential divider used in the RCA circuit. Baxandall claimed to be using a transformer design patented by the BBC (Mayo, Tanner, Ellis). I've seen the same arrangement used in a Marconi push-pull amplifier.

I reckon I'm going to have to adopt the Baxandall arrangement, but would be interested to learn what others think of these circuits. Presumably it was amplifiers like this that inspired the rather quirky Quad 2 extra feedback to the output valves. http://www.drtube.com/schematics/quad/quad-22.gif


Michael