Tube current regulation for series heaters' supply.

[engels]

I've got a bunch of compactron tubes that I want to put into PP use. The heaters on these tubes require various funky voltages (21, 33, 38 V) at 0.45A. I've got pairs of 21GY5 (21V) and 33GY7A (33V).

I thought about building a series heater supply for those tubes which asks for a 45mA current regulator. I haven't done tube current regulators before and I don't even know which type does 45mA. There are nice & cheap octal ballast tubes like URB-001, 002, 003 ... 010 but I miss some explanation how to get a desired current out of them.
Of course, I'm not wiring them to the mains, I will probably use a 24V tranny with 1.5-2A rating.

The first option that comes to my mind is probably 24V AC bridge rectified to 33V for a parallel supply, but I still wonder about tube current regulation.

[SY]

Why use a tube there? The drop is pretty high for these low voltages. A transistor or FET will perform much better in that application.

[d2134]

thought about building a series heater supply for those tubes which asks for a 45mA current regulator.

21GY5 and 33GY7A need 450 mA ! A transistor CCS is more suitable at this current.

[engels]

first, sorry for 45 instead of 450.
0.45A

But don't you think fets also perform much better in the audio output?

[jnb]

Originally posted by engels
But don't you think fets also perform much better in the audio output?

I don't think a solid state current regulator for your heaters is a bad idea as the heaters are not really in the signal path.