It housed 480 valves, all 12AT7 double-triodes. Only 350 of them actually took part in the action; the rest were spares being "burned in". 120 relays drove the displays. A few germanium diodes were used as 'OR' gates. Most of the connections were directly soldered — rather than using pluggable connectors — for reliability. (This, however, made for difficult transportation!)
Unlike most digital computers, then and now, NIMROD used directly-coupled voltage levels rather than clocked pulses, so it could run as slowly as the demonstrator wished. When run at full speed, it was driven by 10kc/s steps [10kHz in modern parlance].
Designing a processor was no doubt rather simpler in those days, but work on the design was begun on 1 December 1950, and it was delivered on 12 April 1951. The Science Exhibition opened on the 4th of May, and ran through September. Unlike transistors, valves burn out, so there were a few failures, but it seems these were easily traced, amd things would be running again in an hour or so. There was one original wiring mistake that early on caused a couple of errors a day, but once this was found it ran flawlessly.
In October Nimrod went on to Berlin for three weeks, to thrill crowds in the Industrial Show there.