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ups.com...
N Cook wrote:

History , there was a smell of burning followed by cutting out.
Next time powered up high pitched squeel.

instability narrows the options.

Now on powering up very muted output like half-wave

I cant think of anything that might be described by both those terms,
so dont know what you mean.

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.

after the preamp? If so that gets the power amp out of jail free.

Before testing the valves etc, anyone have any pointers ?

I'd just start by using a probe to listen to the audio at each stage
thru the chain, see where it goes wrong. Would need to remove the
preamp's nfb path before doing this.

I once had something like this that IIRC ended up being to do with dirt
on a spark gap... but memory is less than sure, and it doesnt sound
like youve got a power amp problem so this presumably wouldnt apply.


NT


I decided to have another look. The distorted and lower level signal than I
would expect was at the input grids side of the push-pull splitter/driver
valve so problem is presumably further back to V1,2 or 3 or op-amps

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