Colossus also has to create bit streams corresponding to the lug patterns set around the 12 wheels on the

Lorenz SZ42 cipher machine. This is achieved by rings of Thyratrons, gas filled triode vales, precessed

round by the regenerated sprocket pulses coming from the Master Control panel on the J rack.

The thyratrons are mounted on the back (outside) of the W rack in the back row of Colossus racks.

The thyratrons are arranged in 12 rings, one for each of the wheels on the Lorenz SZ42 cipher machine. As the rings progress their cathodes can be connected to an output line by wire patches to generate the wheel bit stream. The uni-selectors set the start firing position for a ring at the start of cipher text. The left hand side holds the X and M wheel pattern generators..

The back (indside) of the W rack holds the thyratron rings controller panels, one for each of the twelve rings. These controller panels set the first strike thyratron as selected by the start uniselectors and also quench all the thyratrons at the end of the cipher text. The twelve rings are five X rings, (X1 to X5). Five S rings (S1 to S5) and two M (motor) rings (M1 and M2)

S1

S2

S3

S4

S5