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hi guys
i have just recapped a 1960 watkins [uk ] tape echo using modern filters 22+22+32uf to replace defunct 20+20+20uf can. it works well and sounds good now but the mains hum is still terrible and I wonder if anyone can advise any tricks to minimise this . I was thinking on trying 3x 47uf @450V but i dont know whether this would stress other parts of the circuit [would almost triple stock filter value ] or change the sound for the worse . the unit has 2x 12AX7 and one 6BR8 valve . would greatly appreciate any advice
cheers - rob
Follow Ups:
Did you replace the diodes and the coupling caps? Your hum sounds like a bad part somewhere. Increasing you caps beyond the original spec may improve performance from the original spec, however it would not address a badly humming unit. (By the way, the only additional stress higher value caps would be if you were using a valve rectifier and you over did the first cap, more is the merrier with PS caps in general).
hi chris- i replaced coupling caps and they appear good and not leaky,
i'm not sure if there are any diodes [ the heater circuit apparently is not DC and there is no rectifier ] i also replaced grounds as per before.
everything is packed in close inside the unit and they have a rep for hum but this is way beyond being usable at present time
thanks - rob
Reg,Did you replace the original two-prong cord with a three-prong cord? The green ground wire can actually cause a ground loop, if placed in certain parts of the unit.
The green wire seems to work best if soldered or bolted directly to the chassis as FAR from the star-ground of the circuitry---in a nice open area away from any ground points from the unit.
hi chris
there is a 3 wire plug [ uk ] on the copycat so it looks like thats ok
i'm going to see a nice old guy i know [ good with old electrics,tv's etc] tonight and hopefully he can check through grounds and any other stuff he can do like suppressor caps? - he may have a trick or 2 up his sleeve and is much much more knowledgeable than me
thanks for your time and help
best wishes - rob
hi steve
please see previous post to this which i mistakenly thought was from chris o !apologies and thanks for your advice
cheers - rob
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