Colossus - Valves

[David Simpson]

At Bletchley Park - Does anyone know which were the most commonly used triode valves with topcap connections & IO bases, please ?

Regards, David

[ukcol]

I know that the colossus used EF36 pentodes because I donated some a while back. I don't know if it used any triodes though, but someone will.

[paulsherwin]

Yes, my understanding also is that Colossus was built around hundreds of EF36s. They were just doing logic so you'd expect them to have used lots of double triodes, but I suppose they just used whatever was easily available. The EF36/37/37A always had a reputation as a reliable valve so maybe that was a factor.

[Radio Wrangler]

EF36/37/37A for general small signal use. They used 807s as relay drivers and also used some thyratrons if I remember. The 807s have top caps, but they are beam tetrodes.

David

[BobGreen]

I expect the thyratrons were T41s as they were prolific on the WWII surplus market and captivated my youthful interest to use them a lamp dimmers followed later by SCRs.

[Herald1360]

6J5 is octal triode with top cap grid.

Don't know whether Colossus used any.

[Heatercathodeshort]

The 6J5 does not have a top cap. It is half a 6SN7. J.

[paulsherwin]

I would have expected Colossus to use lots of 6SN7s, but presumably they were in short supply, or designers were reluctant to use an American valve in such a classified project. I don't know to what extent the Americans were embedded at Bletchley - they may have been kept at arm's length.

[SteveCG]

Perhaps Flowers used those valves that he had found by experience to be reliable? Also the choice may have been determined by what Dollis Hill had in stores - and that could be used in large numbers without raising comments?

[Alan Stepney]

It also used large quantities of those lovely little diodes, the EA50, or whatever its CV number was.

I was able to supply them with many dozens of assorted valves for the rebuild of Colossus and for the EDSAC project.

[rayfarrar]

I visited Bletchley Park earlier this year - well worth it. They are still interested in valve donations for Colossus and I did make a note of what they wanted - I'll post it here when I lay my hands on it

Meanwhile there's a very good description of Colossus in this PDF document http://www.cs.ncl.ac.uk/publications...papers/133.pdf from Newcastle University. It shows some circuit samples eg EF36 Adder.

[David Simpson]

Thanks Guys, for info.
Actually, a pal contacted me to see if I had any triodes with a topcap, which would've been used in Colossus. They wanted one for a Christmas present for someone's scientific photographic project, and it didn't matter if the valve was u/s.
I too thought that the ECC3-series of older triodes would've been more likely. The only single triodes I have from that era are GT's. I do have a decent spare working CV63, but obviously don't wish to lose it to a picture project. Likewise - a number of decent 807's. The pictures of Colossus which my pal sent showed a number of Red Mullards, which looked like EL types. However, he's convinced that a red triode valve with a topcap is what this person wants.
I've just had a jolly good clear-out of duff valves, so I'll tell him to try elsewhere.

Regards, David

[DangerMan]

The thyratrons were Marconi-Osram GT1-C type.

Other types used were indeed mainly EF36/37 and 807's, although equivalent types to EF36/37 may also have been used considering the sheer numbers required for all the colossus machines actually made.

[Herald1360]

Originally Posted by Heatercathodeshort

The 6J5 does not have a top cap. It is half a 6SN7. J.

Oops! Should be 6F5G.

Perhaps an EBC33 would do? That's the same red as the EF37s etc.

Just a couple of extra diodes to forget.

Or perhaps an H63?

[DangerMan]

It's worth remembering that colossus was built in wartime and that many of the valves would have been CV equivalents of the civvy valves.
Therefore, many of the valves in the original machines would actually have been "CV grey", not red.

[ukcol]

Originally Posted by DangerMan

...the original machines would actually have been "CV grey", not red.

The only colour pictures I have seen of colossus show large numbers of red EF36s but they would be of the rebuild and that doesn't tell us what valves were used in the original machine.

The secret nature of the project would presumably have been a factor in how and where the valves were sourced.

[n_r_muir]

HI,

Tommy Flowers, the designer of colossus, was a General Post Office employee so I think that the Post Office stores system was the most likely source of the valves

[Refugee]

The EL37A has the grey CV358 as the military equivalent.
I have one that has lost the grey coating and with a bit of T-cut the internal view can be seen.

[jim_jobe]

Originally Posted by Alan Stepney

It also used large quantities of those lovely little diodes, the EA50, or whatever its CV number was.

I've got a box of 50 EA50s they can have Alan. Have you got the address to send them to please?
Jim

[Alan Stepney]

Bletchley Park Ltd
The Mansion
Bletchley Park
Milton Keynes
MK3 6EB