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this is a DeLuxe Reverb clone that i built a year ago, unit was gigged with every week, many times, this past week the PT developed a direct short on primary side, replced unit with a Mojo 761 EX and now i have major hum, that is very loud when all controls are on zero, as volume is turned up it disappears about 1/3 then returns and again disappears at 8-9 then returns at max volume. both channels, also as the reverb is turned up it is present....this is a 60cycle hum...and it does push air, all tubes swapped out, nothing else is or was changed except for the PT....
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The Mojo 761 does not have a center tapped filament supply. Do you currently have a virtual ground for that filament supply? -
that's a very good question, it does not, what do you recommend? I do beleive this could be the problem! any info appreciatedComment
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From each end of the filament winding, solder a 100R resistor to circuit ground. OR, tie each end to the ends of a linear 220R trim pot and the output to ground, with the pot approximately mid-way.vary teh pot very slightly to make perfect center, you'll hear the hum at minimum at this point. this may not be all the 60hz hum, but it'll surely kill a lot of it.Comment
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jmaf, thanks for pointing this out, i even was looking at the schem of the trans and noticed 1 less wire to ground, will install the balance pot method and fill you in on progress.........thank you very much(as Elvis) fesComment
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jmaf, just installed the 200ohm pot for ground/hum balance the reduce hum from mojo PT replacement, it works very nice, thanks again Fester GomezComment
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