In article , Trevor Wilson
scribeth thus

"Dave Plowman (News)" wrote in message
...
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?

Both channels seem to match ok before this happens.

**First off: The "Mains hum" is not mains hum. It is 100Hz hum. It is the
sound made by an amplifier when so much current is consumed from the power
supply, that ripple appears on the outputs.

Second off: You need to ascertain if the output devices get hot with no load
connected. If they still get hot, then look for a fault in the bias section,
or further down the chain. Something is causing the output devices to
conduct too much current.

If the output devices run cool when no load is connected, then it is likely
you have a large DC Voltage at the output. If so, the fault could lie
anywhere in the amp.

Since the fault is 'triggered' by some external issue, it's gonna be tricky.

If you have a link to the schematic, it might be helpful.



Hang a scope on it .. I bet its 'oscillatin at RF somewhere..
--
Tony Sayer