The Colossus Rebuild Project by Tony Sale

Colossus Reborn

The Patch Panel

The Thyratron ring circuits precess round from one Thyratron to the next in the ring driven by the sprocket hole pulses coming from the paper tape reader.

But the continuous stream of pulses has to be converted into a pattern of pulse/no pulse. This is done on the patch panel in the outer part of the W rack.

Small U shaped wire links are used to connect a particular Thyratron cathode output to a common output bus bar through a high resistance.

This gives an "x" in the pattern. No link gives a "."

On the far left just beyond the patch panel the ring start uniselector can be seen. The wiper position in this uniselector determines which Thyratron is struck in the blank interval in the cipher tape being read. this constitutes the pattern "start" position being tested and is the point from which the ring precesses when the start hole in the tape is reached and data starts coming off the tape.

The start position is printed on the typewriter and can be automatically incremented to a new position for each read down the cipher tape.

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.