While we are on a roll with old radars....
The Klystron was powered by the rheostat that used to jam during power up as mentioned in the posts above. The pulses were produced by a piece of kit called a "Hydrogen Filled Thyrotron" (Sp?). This was a piece of kit similar to a fluorescent light tube but filled with Hydrogen. Low voltage pulses provided by an amplifier (parametric amplifier or PA) would hit the terminals and cause the gas to ionise - once ionised it would allow the radar waves from the klystron to be transmitted in sharp edge pulses. No TWTs for the AN/APS 20F. (The "F" bit was a digital video accumulator system attached to the receiver but it didn't work particularly well and we usually stuck with raw radar.
The small radar scopes did not have any afterglow and therefore all responses were marked by a chinagraph pencil. This was repeated scan by scan - if the contacts left a pencil trail at 300 kts then it was an aircraft - 15 kts and it was a ship!
Being a basic pulse radar, we could operate over sea only and the radar was subject to sea returns out to a range dependent upon height and the sea state. At about 2,000ft, we had sea returns out to about 40 miles and so had a useful range against fighter size targets between about 45 and 70 miles (on a good day). The idea was to set up intercepts running at a tangent to us so that we did not lose the contacts due to either the max range or sea return. Even then, raw radar only gave us a return at about 2 positive hits every 6 - the rest were added by DR with the chinagraph.
As PN has stated, we could in theory detect targets out to 200 nm, but this was very rare although the radar loved head-on detections of bears due to the big props and it was not unknown to get early pick-ups on Q.
A good controller had the ability to lie convincingly to the fighter on the radio and pretend that he knew exactly where everything was. (Alpha control was to be avoided at all costs if possible). We had raw IFF to help us - these left an eyebrow behind the radar contact - the angular size of the eyebrow dependent upon the IFF interrogator beam-width which was quite large! To decode the IFF response, we put a video "box" over the eyebrow and this would count the received pulses and work out the decode for us. (The eyebrow was made up of all the received pulses from IFF). The decode was displayed on the panel to the left of the radar scope (to the left of the Orange Harvest in the picture above). An emergency squawk gave us the standard 4 eyebrows! Needless to say, two aircraft in close proximity gave us problems with garble and juggling the fighter behind a squawking target often proved embarrassing.