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In Reply to: RE: AC/DC posted by drlowmu on May 10, 2008 at 20:15:05
((My references this weekend about AC heating was in relationship to using a 2.5 VAC filament. Its one of the reasons why 2A3s are so cool, you CAN successfully use AC heating on them!!))No doubt Jeff, you definitely can use AC on them, and they'll give you -3db on the hum when compared to 5V tubes. That's one of the things that make the JJ 2A3-40 such a cool tube (basically a really nice 2.5V 300B). I was taking objection to your statement about the music going away if you used DC.
((May I offer a possibility? You might well have reached a different conclusion if you were using 2.5 VAC DHTs))
Possibly, we'll never know, but I might add that filament hum, on the 5V tubes using AC, wasn't a factor in the evaluation with my 96db speakers.
((L's for DCed Ef supplies need not be expensive, the Panasonic AC Line Filters are common mode inductors, (their V-850 series), which sell for under ten dollars each and are small and handy. Nice for filtering fixed bias supplies also !))
Yes, it was the Panasonics I was referring to in the last stage of the proposed LCLCL filter. You turned me on to those years ago. However, I think one reason my 1 choke supply sounded as good as it did was the quality of the choke, so there may be something to paying a premium for a real quality inductor there (all inductors don't sound the same even though they may have the same L and DCR). Also I'm pretty sure that the quality of the better diodes and caps had something to do with it as well.
What I was really wondering was: if being able to use smaller capacitors because of more filtering from the inductor was a big factor. I'm thinking that the faster time constant due to smaller caps, while keeping DCR very low, may have been the "magic". I truly dislike electrolytics (I don't even like Blackgates), but they are a necessary evil in DC filament supplies, so I'm thinking that less is best.
I kind of go along with your low everything philosophy, but only to a degree. I think you need enough L to keep the supply from ringing, and enough C to suppress the hum, while keeping DCR as low as possible. There is a fine balance there, just my 2 cents worth.
twystd
Edits: 05/10/08 05/10/08Follow Ups:
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