Wanted: vacuum tube logic circuits

[William Blair]

Chuck Guzis wrote:

> Just before transistors began to be used in auto radios, "space
> charge" tubes made a brief appearance, running their plates and
> heaters from the 12v battery.  No vibrator supply.  Some of the
> earliest transistor designs used a transistor only in the audio
> output stage, among them the Delco "Wonder Bar" models.

> Jeff Duntemann has a nice page on this stuff, along with datasheets:

> http://www.duntemann.com/12vtubes/12vtubesindex.htm

Yes, I found that excellent site back when I was playing with low-voltage tube headphone amps and I have a copy of the Tube Collector Magazine "Car Tubes" article cited there.  However, the tube amps I built from modern plans were ones that used common dual triodes like the 12AU7 but with _very_ low plate voltages.  The reason for this is the scarcity and, as a result, expense of the low-voltage "car tube" types most useful for audio amps and, unfortunately, logic circuits (12U7, 6GM8).  If for some reason I can't get any of the most common and cheapest high B+ dual triode tubes to work in a logic circuit at low plate voltages, then I'll have to go with something like the dual diode, single triode "space charge" car tubes that aren't in demand by audio enthusiasts making them much more readily available and much cheaper.  A functional hobbyist demonstration of tube logic that's cheap and uses low voltages is my goal.