Directional antennas need some form of monitoring and this unit was a best-seller for years. It was a huge improvement over the RCA and Andrew units that preceded it. Stable and reliable.
This one had a few odd problems. A quick look inside uncovered mouse damage. Mice love transmitter buildings and will eat wiring, as they did here. Several control wires needed to be replaced, others insulated.
The FP capacitors used are no longer available, but they make fine binding posts for replacements. Ebay turned up a new switch cap and it’s back in service. The mercury wetted relays used in these units are no longer available. The SCR’s are also becoming scarce.