The Colossus Rebuild Project by Tony Sale

Colossus Reborn

Part of a Thyratron Ring

This shows a close-up of part of the K5 ring of Thyratrons on the W rack.

By early 1996 I had gathered together enough GT1C Thyratron valves to attempt two ring circuits. I chose K5 with 23 elements and K4 with 26 elements as being the shortest rings. I built the plates to hold the Thyratrons and mounted them on the W rack at a convenient working height, (not their correct places). I also constructed two Thyratron ring control plates and with great difficulty got them working.

But the heaters of the Thyratron valves required lots of amps at 4 volts. I had managed to acquire a number of ex GPO 6 volt 70 amp mains transformers and Paul Bruton (now sadly deceased) laboriously took these to pieces and rewound them to 4 volts for me. They are mounted one above the other up the centre of the W rack.

This Thyratron rack with its 501 valves consumes about 2.5 Kwatt of power, most given off as heat. Rumour has it that the WRNS who operated Colossus strung a clothes line above the W rack and used the heat to dry their smalls.

Being of a later generation when computers had cooling systems, I asked the WRNS what they did in the height of summer to keep Colossus cool; "opened the windows stupid".

This page was originally created by the late Tony Sale, the original curator of the Bletchley Park Museum, and Secretary of the Bletchley Park Heritage Society.