vac tubes / was Re: Schematics of Atanasoff-Berry

[William Blair]

William Donzelli wrote:

> >  I've got several homemade variable DC supplies,
> but they are all limited to 1.5A output which would be
> exceeded with just three 5BK7A filaments @ 600mA each.
> 
> An old filament transformer would solve all your problems
> in this area. Not expensive.

Can't get much cheaper than effectively free for a well regulated, high current DC power supply using a modified PC power supply that isn't otherwise being used.  Plus, the idea of using tubes with 5V filaments instead of 6.3/12.6V reduces the competition with typical audio tube customers and makes the use of a high-current 5VDC supply possible. For the homebrew 1.5A adjustable DC supplies, I use LM317HV based units plugged into a homebrew chassis where I've mounted a range of three different inexpensive, surplus, multi-secondary transformers with output voltages ranging from 70VCT to 12.6VCT.  The chassis has binding posts for each secondary and I just plug the banana plugs for the various inexpensive LM317HV adjustable DC supplies into whatever AC outputs most closely match the DC voltages I need at the time in order to reduce the power dissipation requirements of the LM317HVs.