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Folks,
I intend to put a 30mH bead type 4A inductor in 390B and 845 filament.
The intention is to reduce HF noise in the DHT filament
Use common mode or differential mode, if common mode is used then how to implement
Saw some old post but still cannot figure it out
Follow Ups:
For a DHT filament you would want to reject common mode noise. Common mode noise current is effectively in series with the filament and modulates it as a single element, relative to the grid.
Hi TK,
I never implemented common mode choke in filament, here come a question
I intend to use 30mH 5A common mode inductor for 845 filament, but by using XL=2xPix freq x L, it comes to XL= 9.42 Ohm
If now AC filament10V go through this choke, would it drop by 9.42x3.25=30V
If that is the case the common mode inductor has no use at all, or it should be other thinking?
The AC current powering the filament is differential. A bifilar-wound common mode choke should have little effect on that.
Do you have a HF problem? And where dos it come from?
Hi, At the moment no, I just want to do better
I think you have to look at it as that piece of the normal filament supply design and choose your frequency targets. The application note papers (see Coilcraft for one example) show curves and frequencies and discuss tradeoffs and self-resonances, etc. Actually, I think Rod Coleman's or Guido Tent's (etc) supplies are basically a "solved problem" and filter well from most reports. I think the latest versions of Rod's are very adjustable as well. Unless you want to do the work just to do all the work, it makes sense to take advantage of all the refinement those people have been doing for years and years.
Re that schematic, I'm not sure I'd ground those caps across the thing, there, either. Could be a single across both legs (that floats). I remember Thorsten did that stuff years ago in the Lady Day 300B's...see if you can dig-up a schematic for that thing. There should be a lot of discussion here in the archives for those. FWIW.
Common. Maybe only 3 ways to wind and 4 ways to hook it up :)
If they're both wound the same sense, I think (total guess) you'd try the bottom one (happily awaiting corrections)
Hi,
1. What value of the cap after the common mode choke ?
2. The diagram show it also has differential mode choke before the common mode, is it worthwhile or the filament should only cater the common mode noise ?
Hi Grindstone,
The phase is shown in diagram
Are the common supposed to reject the high frequency garbage?
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