Phil mentioned....
Peter J. Walker sure knew what he was doing when he went with cathode
feedback for that output stage rather than UL or similar.
..... Phil
He sure did know, there is no doubt. I am not 100% sure that you know exactly what all of his thinking was, and maybe nobody does because of concerns about being private for good reason. But he also had an ego, and wanted to be original, and profit by claiming superiority. Its OK, human nature.
In another post Phil calls me all sorts of names but does nothing to me.
I have meanwhile re-edited my page
http://www.turneraudio.com.au/quad2powerampmods.htm
I measured the THD Vs Po for an original Quad-II in good condition and for open loop and for closed loop, AND I added the graph for Dynaco MkIV with similar class AB loading to make the comparison fair.
I also re-drew tie THD I got with KT90 used to replace KT66 in a reformed amp.
Whatever anyone wants to know about Quad-II is at my page, including a full description of the OPT which is wound extremely well. Except that it is too small, with winding resistances a bit too high. And Peter left out one extra
terminal to allow wasteless sec windings for 4r0 strapping. But upon consideration, and after drawing a graph for Po vs RL for the 3 possible OPT strappings, the performance when yellow speaker wire from output terminal is connected to Point Q is OK, even though its rarely mentioned anywhere.
However, winding resistance, ie, the resistance of copper wire is benign and Peter Walker knew nearly everyone did not need 20 Watts, so it does not matter that the tubes make 25Watts while putting out 21Watts to the load.
Patrick Turner.