Phil S. wrote in message
...

"N Cook" wrote in message
...
History , there was a smell of burning followed by cutting out.
Next time powered up high pitched squeel.
Now on powering up very muted output like half-wave and sometimes a
burst
of
high frequency squeel but all at low level.
Nothing obviously burnt or over-heated inside.
Stable HT voltage. 4x 6L6
Same distorted sound on the line out.
Before testing the valves etc, anyone have any pointers ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



And you can't find where the burning took place, either by visual
inspection
or smell? (I see your statement above.)
You think maybe someone let the smoke out of the output transformer?
Desolder the leads and test it.



THe owner smelled burning, I have'nt so far.
Resistance checks on the matching transformer seem ok.
All anode voltages seem ok.
Not the slightest sign of overheating on any resistor.
It all looks perfect inside except the pcb polyester is covered in marginal
scratches, like left by a dvm probe tip. But they are all over parts of the
main board and go under the comps, never seen anything like it, presumably
cosmetic damage at manufacture.
I've not met optocouplers in a valve amp before - anyone know details of
their construction used by Crate, 4 lead, not DIL packs ?
Will check through the preamp tomorrow

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/