Salient-pole synchronous 1,800 rpm Rotary Gap featuring 12 rotary 1/2 inch tungsten electrodes on a 10 inch diameter phenolic disc.  The motor is housed underneath the top of the base and is coupled to the rotary disc axle with a positive-drive timing belt.       Close-up view of the GPO-2 Rotary Gap.  The cooling fins on the stationary electrodes are turned from 1.5 inch diameter brass round stock and silver-soldered to the 1/2 inch diameter brass electrodes.