Vacuuum tube digital circuits (50 year rule)

[Brent Hilpert]

Stan Barr wrote:
> 
> Just for informational purposes:  12AU7s (and 12AX7 and 12AT7) are still
> available new.  You probably won't like the price, but they're still in
> production - us electric guitar players use them,

Note that for flip-flops one should 'properly' be using types such as 5963 or
6211 ("computer tubes") to avoid the cathode emission problems which results
from one half of the flip-flop being in the same state for long periods (IIRC
it was the one at cut-off). (Perhaps not a problem for a clock, I don't how
extreme the asymmetry had to be before the problem showed up.)