Curing unwanted oscillation
 

As you may have seen from the Vintage Radio (domestic) section, I sought help in curing a severe case of unwanted oscillation in my recently restored Pye QAC2.

The problem was helped by wrapping copper wire around the bottom of V2 (Every Ready A50P) but the oscillation was still bad. I prodded and poked about in the wiring and this did reduce the problem but did not remove it.

On turning the chassis right way up and approaching the top cap grid of the output bottle (Pen4DD) the oscillation was reduced further and by grasping the lead to the top cap, further still. The set now worked ok at lower volumes but came on again as the volume control was advanced.

As the top cap lead wasn't screened, I replaced it with a bit of audio co-axial which as it's black doesn't look much out of place. This was earthed only at the chassis end. This cured the problem completely and the set now performs fautlessly.

Worth giving a go if your set exhibits similar problems

Re: Curing unwanted oscillation
 

Nice detective work, some grid top sockets also have a stopper resistor of a few k there to stop parasitic oscillations.

Re: Curing unwanted oscillation
 

Yes, it could make good sense. I'll try it with a set I've got here with this problem.