The Level-Loc is a brickwall limiter made by the Shure microphone company for public-address-system use (podium mics, specifically) in the 1960s.
It uses discrete transistors and transformers in the signal path; it offers balanced mic-level i/o and an unbalanced consumer-level 10K ohm impedance output as well. There is an input-level control (simply a pot that follows that secondary of the input transformer) and a switch marked ‘distance selector,’ which seems to me to be a threshold control. That’s it for control. It is fairly noisy (full-bandwidth noise), even after a recap, and the transformers are not especially well-shielded. It runs off of a 9V battery.
The Gear Rack