Adjustable cathode bias?

I could not find that info on mouser datasheets. But 1 mA is very small current. At the worse position 10K 1mA the power dissipated is only 0.01W.
I would go with a wirewound 1W and call it a day.
 
I'm fairly certain the bias pots on the VTA driver board I'm using in one of my amps aren't anywhere near 1W rated, and they've been fine since I built the amp. Granted, it's maybe been a year on my amp, but I'm unaware of any reports of premature demise of the bias pots on the VTA driver board.
 
I think mine is Class A

if its class A, I don't think EFB will do much for you. Its meant to help correct for power supply sags, particularly in the screen supply. Class A runs a pretty constant average load so there won't be much for it to do. It will still work as a means of providing a bias adjustment but thats about it.
 
if its class A, I don't think EFB will do much for you. Its meant to help correct for power supply sags, particularly in the screen supply. Class A runs a pretty constant average load so there won't be much for it to do. It will still work as a means of providing a bias adjustment but thats about it.

Yeah, and same basically goes for fixed bias right?

I'll be right at the upper end of the tube dissipation so regardless that fixed bias would make more B+ available, there still really isn't any more to gain by that avenue since it's pretty much maxed out in Class A anyway. True?
 
It seems to me that the fact of you having some issues implementing your bias scheme indicates that it is probably something other diy'ers and manufacturers ran into as well. otherwise we would see its design more often. After all biasing a tube has been worked on since tubes were invented. On the other hand if this is an exercise or design that you feel you need to work through for your whatever reasons, then i am behind that 100% and hope that it can yield positive results.
 
It seems to me that the fact of you having some issues implementing your bias scheme indicates that it is probably something other diy'ers and manufacturers ran into as well. otherwise we would see its design more often. After all biasing a tube has been worked on since tubes were invented. On the other hand if this is an exercise or design that you feel you need to work through for your whatever reasons, then i am behind that 100% and hope that it can yield positive results.

I'm not having any trouble...nor do I really expect any. The implementation is perfectly clear to me. It's simply a 500 ohm resistor in series with a 100 ohm rheostat. The only thing that could be more simple is just a single 560 ohm resistor per tube and no adjustment as originally planned.

It's something I thought of to add a hair bit more improvement for balancing two parallel tubes. In hind sight, I probably would need to add the adjustment to only one side..but then I'll have a subconscious symmetry of build concern. LOL.

This is just to give a small adjustment for final balance, it's not intended to give a full range of adjustment.
 
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I've use it wirh success in a 6V6 mono amp, I just used a tapped wirewound resistor. Of the type I posted above.

And I have a Devry amplifier from the 40s with a similar setup. This isn't unheard of, it's just that self bias works pretty well, and there's usually no need to dial it in so precisely.
 
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