"Dave Plowman (News)"

Got an 'interesting' fault on an ancient Linsey Hood amp. Switch on a
light etc, and sometimes *one* channel bursts into loud mains hum - but
carries on working. And the output transistors get very hot. It's not
normally susceptible to mains born interference - so any guesses before I
rip it apart?


** Pretty much guaranteed to be supersonic oscillation of the output stage -
easy to see on any CRO or " scope " as the Yanks insist on calling them.

Lotsa possible causes, but I would start with a careful examination of the
zobel (ie RC) network at the speaker output part of the circuit. The cap
and or resistor may be open circuit or have bad soldering.



..... Phil