Re heaters elevation

[catalin gramada]

9Hello. May be heaters elevated from ground in a CF circuit directly from cathode of its stage please ? Meant, in case we have a dedicated heaters transformer for a CF stage may just reference the heaters connecting heaters winding center tap directly to its cathode, meant Vhk=0V no matter how high the cathode is above the ground...??? Thx

just like that. There is a chance to modulate the signal with ac heaters freq in this case ? Something usable please ?

[pdf64]

I think that might work ok. Obviously the heater winding can’t supply any other heaters, so it seems something of ‘a sledgehammer to crack a nut’ scenario.
I there were any problems, eg modulation, perhaps change the 100ohm to eg 10k and decouple the winding CT with say 2u2F.
I’m assuming the valve is an ECC 81 or 82? Both sections in parallel?

[Helmholtz]

If there were any problems, eg modulation, perhaps change the 100ohm to eg 10k and decouple the winding CT with say 2u2F.

That would load the CF output with ~10k, stealing a considerable part of the available output current.

But I don't think filtering is necessary. The situation should be comparable to directly heated tubes.

[pdf64]

That would load the CF output with ~10k, stealing a considerable part of the available output current....

I was thinking that would be the case for ECC83, but that a ECC81 or 82 section, perhaps even a parallel pair, might cope ok?
If not, then take it up to 100k.

[catalin gramada]

Is a CF 12au7/12bh7 type experiment. Think elevation directly from cathode as a solution may be but cannot figure how to implement in proper way, if possible. Few turns to make individual windings for each heaters is the last problem I have. For parallel arangement or single of course. Thanks for input.

[Helmholtz]

I was thinking that would be the case for ECC83, but that a ECC81 or 82 section, perhaps even a parallel pair, might cope ok?

Idle current is 9mA, so max. no load current swing is 18mApp or 6.5mArms.
A 10k load would consume 2/3 of the available current.

Can't say if this is a problem in the application.

It's quite disappointing that while the cathode output has low source impedance, it can't supply any more current than a plate output.