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Old 15th October 2006, 02:03 AM   #1
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Default DC filament

I have build my tube amplifier this summer, I used kapton wire (very hard to twist..) so I skip the part of twisting wire... Now it`s intalled it induced a 60hz buzz... Can I use a rectifier and use DC circuit to heat my 6L6GC filament ? Thank
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Old 15th October 2006, 02:09 AM   #2
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are you sure it's the filament transformer that does it? I'd check grounding first.. (picture please)
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Old 16th October 2006, 08:25 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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Have you grounded one end of the filament transformer secondary? Try that first.

Also try connecting your signal, power and output earths separately, then running them to one point (star grounding.)
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Old 16th October 2006, 11:04 AM   #4
bembel is offline bembel  Europe
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here's a trick to twist wire (even hard one)
hook the wire pair (or more) in-between a clamp and a drill's chuck.
Then use the drill !

hope this helps

PS: anyway, you can use DC to feed your filaments, but there's a lot of current needed in power tubes's filaments.
Anyway input tubes are more sensitive to filaments hum and use less power to run their filaments, that's why usualy DC supply of filaments is only done in the preamplifier.
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Old 16th October 2006, 11:14 AM   #5
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Before going through the trouble of making a DC supply, make sure the filaments are the cause. Try the above advice. Failing that, try floating them +40V or so above ground with a voltage divider from the B+. If that fails too (usually doesn't), then you could go nuts on a DC supply...
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Old 16th October 2006, 02:15 PM   #6
vax9000 is offline vax9000  United States
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The hum might not be caused by the filament current. The output transformer can directly pick up the 60Hz magnetic field. Try to disconnect the primary of the output transformer and check whether there is still hum.
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