Vacuuum tube digital circuits (50 year rule)

Allison ajp166 at
Thu Aug 31 06:25:04 CDT 2006

>Subject: Re: Vacuuum tube digital circuits (50 year rule)
>   From: "Ethan Dicks" <ethan.dicks at>
>   Date: Thu, 31 Aug 2006 17:55:47 +1200
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at>
>On 8/31/06, woodelf <bfranchuk at> wrote:
>> The ads list a 12au7 for about 65 cents in 1955. In 2006 a generic 12au7
>> is about $8.00. I suspect a better deal now than 50 years ago.
>Hmm... if I leave off seconds and just go with minutes/hours, I think
>I have enough.  Even with modern wages, a bag full of tubes costs
>enough to make me want to simplify the design.

Hunt a bit I've found Vacuum tubes NOS (New Old Stock) to be widely available.
The prices vary widely.

To do time.. 12:59 should give you a hint.  You need 3 counters only one
is decade.  the tens of minutes is 0..5 (/6) and hours is either /12 or /24.

>The real trick, now, I guess, is how to take 60Hz mains and clock it
>down to 1/60Hz with 1955 technology.

You need a decade counter and a /6 counter for that, same general circuit 
just no disply.  For simpler you can use several retriggerable monostable 
with time out being just longer than say 10 cycles and a second with
time out of >6 cycles.  At most three tubes to do that (12au7/12ax7/12at7).

Back when Grumman plant-33 closed (LM project) I picked up a Beckman EPUT
(events per unit time) and it was basically 5 digits of that style counter
(counted to 5mhz, 8 on a good day) a time base and input circuits (Schmidt
trigger).   All tubes!


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