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In Reply to: RE: Filaments and filament bias posted by Tre' on April 15, 2016 at 08:37:33
I'm talking about a 26 in filament bias. As I said, in filament bias the DC current reg - in this case Rod Coleman's reg which is floating - is connected at the plus side to one side of the filament, and the other side to ground. The other side of the filament goes to ground through the cathode resistor. So the current reg goes through the filament and then through the cathode resistor.
The audio signal also goes through the cathode resistor. So the total current going through the cathode resistor is 1 amp for the filament plus e.g. 6mA for the audio signal.
That's how filament bias works.
Follow Ups:
"I'm talking about a 26 in filament bias."Of course you were. I should have known that.
I don't know how I missed that.
Sorry Andy.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/16/16
There's a lot of users now that would consider filament bias the new standard for tubes like 26, 4P1L, 01A and probably 10Y as well. No cathode bypass and a resistor nor much larger than 10 ohms is a nice design option. It's a great choice for output tubes as well, if you use 4P1L.But it's a DHT choice, and once the bias gets too high combined with an amp or two of filament current, it's just not possible or practical. So no good for 45, 2a3, 300b unfortunately.
But what it does, it does really well. Thomas Mayer popularised it and Rod Coleman created filament regs that made a clean DC supply cheap and easy. A lot of us jumped on the bandwagon when we saw the advantages. I've been using it since around 2009 now in all my amplification. Rod's designs started to be published around 2010. Seems a while ago now.
Edits: 04/17/16
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