I'm having another look at the little SE 6BQ5 amp I got from a scrapped record player. The original schematic is attached to this thread. http://www.audiokarma.org/forums/showthread.php?t=514623 The feedback went via the tone and volume pots. Another feature is that the output transformer has a tapped primary and the B+ at the reservoir capacitor (C67) immediately after the rectifier goes to the tapping on the transformer at a point on the secondary so that the ripple current flowing in the output valve anode cancels with the ripple in the B+ current flowing to the rest of the amp including the smoothing capacitor (C50). This makes it nice and quiet in operation. When I removed the tone controls and made it a power amp to use with a 50k pot, I used the values of the attached schematic. It works, but now I don't know where/how to apply feedback! Without feedback there is some high frequency distortion. If I apply the 22K feedback, either to cathodes as in the 'new' circuit, or the grids as in the original one, it oscillates with HF. So, I'm thinking of starting again. Any favourite schematics?