5E3 HUMmmmmm

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zachsdad
Posts: 3
(3/30/04 5:18 pm)
 5E3 HUMmmmmm
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 My first scratch built. Great sound, but a low level hum.--Even with all the tubes out. Definitely coming from the speaker. OPT and PT are about 2 inches apart and at 90 degrees. Any ideas or fixes.

Leslie
 
bnwitt
Senior tube assistant
Posts: 308
(3/30/04 9:54 pm)
 Re: 5E3 HUMmmmmm
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 Did you follow Doug's grounding scheme? Do you have anything grounded to a PT bolt?
 
zachsdad
Posts: 4
(3/31/04 7:54 am)
  HUMmmmm
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 Followed Dougs grounding scheme. No PT bolts used. Filament wires twisted and in phase. Filament winding center tap is riding on DC via cathode of output tubes. I had this grounded previously and saw no change in hum. This is not a very loud hum, just enough to be annoying. Maybe I'm expecting too much. What swamps me is that the hum is there with ALL tubes removed, and the intensity doesn't change when they are installed. Is there some way to shield between transformers? Does it matter which end of the OPT primary is grounded or if it is grounded?

It's really good to have this forum and this bunch of guys to bounce these problems off of. Much obliged.

Leslie
 
bnwitt
Senior tube assistant
Posts: 309
(3/31/04 9:58 am)
  Re: HUMmmmm
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 Is the hum present when both volume controls are on zero? When you say which side of the OPT is grounded, do you mean the speaker out secondary wires of the OT(output transformer)? Typically the black lead is grounded and the green lead is to the tip contact of the jack. I had a hum problem in my first 5E3 with the black wire going to a chassis ground and when I switched it to just the ground terminal of the speaker jack(which then grounded only through the jack body to the chassis) the hum went away.
 
Crispycircuit
Junior tube assistant
Posts: 15
(3/31/04 10:01 am)
  Hummmmmm
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 If it hums with no tubes, then it's inductance. I would guess the speaker is too close to the power tranny and is inducing 60 cycle hum into the speaker.....Try a different speaker away from the tranny....
 
Lucid Alice
Senior tube assistant
Posts: 183
(4/1/04 10:27 pm)
  Re: Hummmmmm
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 With the tubes in, does it hum in standby? If it does it is your OT placement. Unbolt the OT and move it around. If you can get the hum to stop you will have to relocate the OT.
 
 
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