Amp seems to work perfectly well, being repaired for minor problem, no
succeptibility to microphony or tinging distortion.
Testing the 2x EL34, gains are good and matched but after a minute on
heated C/H insulation check, the resistance gradually decreases to 1M for
one and 0.5M for the other.
What problems will this lead to if continued use, and how quickly ?

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