Swinger buzzing intermittently

Design and use of Chokes for PS, anode and filament use.
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pjanda1
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Joined: Tue Oct 20, 2009 12:26 am

Swinger buzzing intermittently

Post by pjanda1 »

Dave,

I've got a giant old Stancor swinger as the input choke in my 6V6 PP amp. It has a little cap in front of it (.22uf, IIRC), and a big resistor in series to maintain critical current (tried both 10K and 15K 50W). He is pretty mechanically quiet most of the time (on rubber isolation feet in a partially enclosed chassis), but intermittently, while the amp is amplifying, he goes into a short lived buzzing fit (loudish). Maybe once every 2-3 minutes for a few seconds. He doesn't seem to do it while the amp is idling, but I could be wrong. It doesn't seem to be in relation to anything else.

This has been going on for awhile, and it is driving me nuts. Is it just a bad choke? Is there some sort of amplifier problem that could contribute to this? PS iron has been driving me nuts with this amp. I'm on my third power transformer and this is the second first choke. If I'd just buy nice instead of trying to recycle old iron, this probably wouldn't happen to me!

Paul
dave slagle
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Post by dave slagle »

hey,

swinging chokes work by taking advantage of saturation. When the DC Flux exceeds the AC flux the core remains quiet but when the AC exceed the DC they can get noisy.

Is the amp Class AB? could the buzzing start when you hit class B and modulate the current draw?

dave
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pjanda1
Posts: 3
Joined: Tue Oct 20, 2009 12:26 am

Post by pjanda1 »

I know the easy way to answer this question is to take it down to the bench and watch the current draw through the PS, but that sounds fairly boring. A) I don't think I'm ever hitting class B. B) if it were, wouldn't the buzzing then occur in relation to the dynamic level of the program material? It doesn't seem to matter whether it is playing softly, loudly, or not at all.

I figured it would be related to current draw, but I also figured that swapping the "bleeder" resistor across it from 15K to 10K would then make a difference.

Paul
pjanda1
Posts: 3
Joined: Tue Oct 20, 2009 12:26 am

Post by pjanda1 »

BTW, I've been paying more attention since we talked on the phone. I think the choke is really only unhappy during the day, and behaves much better at night. So, it is probably related something on the AC line.

Paul
www.wildburroaudio.com
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