Ron(UK) wrote in message
...
N Cook wrote:


Its external mains bourne dimmer type noise but not hum in the mostpart.
Whether inside cabinet with mesh closure or outside with improvised
closure
shield. Not internal crackles.
All input null shorts are fine.
I may try the suggestion of an isolating and balancing feed of 110V to
the
amp just as a try out as simple to arrange temporarily.

I generally find that I get more hum and noise using the isolating
transformers on my bench than I do when an amplifier is connected
directly to the mains.

Ron(UK)

With only the main HT and next "B" supply to the 2x 6L6 and the
splitter/pre-driver , remainder disconnected, there was normal amount of
noise.
Similarly reconnecting all the supplies but pulling all the valves except
the first stage amp valve and those last 3, so basic "clean channel" amp
then also acceptable amount of noise.

Trying with an isolating 240V to 55-0-55V transformer with 0 grounded
feeding the 110 V transformer of the amp and full compliment of valves and
function ,then no reduction in noise performance from autotransformer feed
situation.
It seems I have to confirm that the auto-transformer is wired to take 110V
off the neutral end and not the live end of the 240V, to feed the original
USA isolating 110V.

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