Decca SRG899
I've recently been restoring one these grams for a chap who's into 70's retro furniture and equipment. The performance is actually very good in terms of volume, tone and overall features, but it was suffering from a raucous hum on both channels even at zero volume, more pronounced on the left channel. That should have told me something but I missed the obvious. I went through the usual checks for earth loops, faulty capacitors, badly positioned cables etc. to no avail. Then I noticed what should have been obvious from the start (not thought of as Decca equipment was usually very well designed, but not in this case!) The mains on/off switch is adjacent and very close to the scratch filter switch which is in circuit regardless of being set for gram, radio or tape. and the filter capacitor for the left channel was actually laid on top of the mains switch. Just moving that helped but a much better result came from adding a metal screen between the 2 switches - see pictures. I insulated the mains switch side for safety.
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