Anybody who has seen an old Airco track burner or pattern cutter has seen the speed controller with the letters instead of numbers.
These are made by Lee Engineering of Milwaukee WI. They have remained unchanged for about 40 years at my guess.
I have taken apart several of them, and for the life of me I can't figure out how they work.
As far as I know all that happens is the dial pushes the tab down in the middle, while the whole piece spins on the end of the motor shaft. There are 2 brushes that rub on the underside, and connect to both sides where the 2 spring arms touch.
As the lever is pushed down in the middle, the 2 arms are slightly deflected.
I just can't figure out how this thing adjusts the motor speed.
Anybody have any ideas?