vac tubes / was Re: Schematics of Atanasoff-Berry

[William Blair]

Chuck Guzis wrote:

> > 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 digital circuits (I assume that's what we're
> still discussing), why is a DC heater supply necessary?  

Because I don't want to hear 60Hz hum when I plug my headphones into the flip-flop output. ;-) Seriously, you are absolutely correct that AC could be used for the filaments in this case, but the PC power supply is being built for multiple uses and will just happen to be there for these tube logic experiments.  I planned to mod the PC power supply well before coming up with this low voltage tube logic project (which may or may not succeed).  My goal is also to provide a commonly available, cheap and multi-use power source for the tubes that could be duplicated by others if I succeed in this and decide to put the tube logic project on a web page.  Like me, rather than just building a supply that would be used only with the tube project, they would be building a very cheap, high-current DC power supply useful for other purposes.

> If you do decide to use a regulated DC supply with
> overcurrent protection, keep in mind that cold heater inrush current
> can be substantially greater than the nominal heater current
> rating.

Right now, my goal is to build just an astable multivibrator clocking a 4-bit counter.  To show the alternating state of the multivibrator, I'll light the tube from below through the hole in the center of the socket with a two-color LED and the states of the counter tubes will be indicated by lighting them from below with a red or blue LED.  I've got the special effects visualized, but that's the really easy part.