21-10-2023, 07:20 PM
Although I use valves quite a bit I've never had anything to do in practical terms with directly heated ones so I may be making a silly beginners mistake here.... but the reason I'm talking about floating CCS 's, one for each valve, (and a couple of silicon diodes across each filament to prevent over voltage), is that audio, probably multistage high gain amplifiers, is my main interest here (I'll have to do a superregen though! 
) and surely the heater IS the cathode hence all valves would "see each other" through the heaters/be cathode coupled to each other, at least partially, if not isolated from each other AC wise? I may well need to take NFB back to the cathode of the first stage for example.
Obviously the usual filament chokes as used at RF would be useless at audio frequencies. In fact some probable uses I may have would incorporate DC feedback so even a truly huge choke would be no good.
The only thing that springs to mind otherwise is that all valves would have to be grounded cathode at AC, no degenerative cathode feedback allowed, and each valve in fixed bias... Hmm come to think of it that's probably why there was a separate bias battery in early 2V accumulator powered heater radios
cathode followers and GG could be "fun"!
If that's the case then being limited to fixed bias grounded cathode would limit their usefulness to me somewhat. I guess RF powered heaters from multi secondaries could be another solution.
) and surely the heater IS the cathode hence all valves would "see each other" through the heaters/be cathode coupled to each other, at least partially, if not isolated from each other AC wise? I may well need to take NFB back to the cathode of the first stage for example.Obviously the usual filament chokes as used at RF would be useless at audio frequencies. In fact some probable uses I may have would incorporate DC feedback so even a truly huge choke would be no good.
The only thing that springs to mind otherwise is that all valves would have to be grounded cathode at AC, no degenerative cathode feedback allowed, and each valve in fixed bias... Hmm come to think of it that's probably why there was a separate bias battery in early 2V accumulator powered heater radios
cathode followers and GG could be "fun"!If that's the case then being limited to fixed bias grounded cathode would limit their usefulness to me somewhat. I guess RF powered heaters from multi secondaries could be another solution.
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