Working order but an intrusive mains buzz on the clean channel, not the same as stray mains pick up, its like picture on sound buzz on a TV. Buzz at most on minimum of gain pot and least on maximum. No effect on buzz , altering the other pots. Valves check out on tester fine, no change in buzz swapping them around. No problems on any switches, pots or sockets. Soldering looks fine, No noise on the HT line. This preamp must have been used in heavy rain, or something like , with the previous owner. Had to drill out one of the casing screws to get inside. Present owner has not had problems for the couple of years in his hands.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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