The Colossus Rebuild Project by Tony Sale



Colossus reborn

The Counter Control Panel

The Counter Control panel is in the centre. The box below has on its face the set total switches, one vertical set, unite, tens, hundreds and thousands, for each of the five counters on the other side of the rack.

Above the Control panel are two of the five dump relays. These multi-contact relays dump the count standing on a counter onto the holding relays on the Relay Rack when the paper tape reader has read all the cipher text and reached the stop hole on the tape.

The Counter Control circuits take the resultant signal coming from the logic circuits and sample it on the leading edge of the sprocket hole pulse.



The resultant pulse, either there for a one or nothing for a zero goes to be counted by the four decade counter on the other side of the rack..

Also on this panel are the comparitor circuits between the setting of the set total switches and the outputs of the four decade counter.



The comparison can be for greater than, equal or less than. It is usually tested at the end of cipher text to suppress printing if the count has not exceeded the set total.

The large 807 valve, top right on the panel is used to reset the four decade counters to zero.

It appears in the circuit at the bottom just left of centre. It is labelled V14, which is the end valve of the top row of valves and this was how the position of the panel was found on Colossus



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.