vacuum tube computer

From: Dave Dameron <>
Date: Sun Jan 31 11:24:32 1999

At 08:02 AM 1/30/99 EST, John wrote:
>Hi all,

>Therefore, I decided to design and build a complete computer with
>vacuum-tube technology from scratch. A short description of the project is

>Program code is 24 bit wide, i.e. each operation
>occupies two 12 bit words. The first word is the
>opcode, the second word is
>a. the address or
>b. an immediate value
>Three 19" racks are used. The bottom of each rack
>holds the power supplies (good old Seymour style),
>the upper parts a total of about 30 card cages for
>standard Euro cards 100 mm x 160 mm. Each cage can
>hold up to 14 cards. Standard 19" mechanical
>components are used for cost and availablity
>reason. Ventilation is by off-the-shelf 19"
>ventilator assemblies.
>There are four types of cards:
>a. logic and registers (approx. 200 used)
>b. clock drivers (approx. 25 used)
>c. core sense amplifiers (12 used)
>d. core drivers (19 used)
>Types a,b use the same printed circuit board, differing
>parts mounting. Types c, d are different.
>The tubes used have been selected according to
>availability of surplus stocks. Starting from
>surplus stock lists, the most suitable tube for
>each purpose has been selected, resulting in average
>cost of less than 1 US$ per tube.
>Types a and c use 6BQ7A miniature dual triodes,
>two per card, approx. 400 tubes total.
>Type b uses 6CW5 miniature power
>pentodes, two per card, approx. 50 tubes total.
>Type d uses 40KG6 beam power pentodes, four per card,
>76 tubes total.

Sounds like an ambitious project! Maybe you can find valves like 5963 which
is a computer version of the ECC82 or 12AU7. The prices of these hasn't
been driven up by vacuum tube audio people.
Am amazed you couls build a computer like this with ~400 cards ~800 tubes.
That is similar to building a complete computer with 200 SSI TTL chips like
a 7400. Especially since a 24 bit latch could use 24 of the cards. I tried
a design once (on paper) with MSI ic's like 74193 counters, and it quickly
got out of hand, 100's of ic's.
It has been in the back of my mind to build something with
relays, discrete transistors, or even RTL (Don Tarbell did this, which got
me interested in him initially).

Have you seen the book, or web references just posted here, of the book
"Computer Structures, Readings and Examples", by Gordon Bell. There is a UK
computer described there, Pegasus, built with valves in 3 bays. It has
approx 400 cards with 3 valves/cards, and is from about 1956.
Received on Sun Jan 31 1999 - 11:24:32 GMT

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