Professor Motor Controller Identification

[red73mustang]

I have a few of these PM controllers with the the knobs and was wondering what model these are and what the knob does. I assume it's for braking or throttle response. There are no model numbers that I can see.

Thanks, Chet

[arroldn]

That one knob is sensitivity control. Or as some might say throttle (trigger) response. Looks like a 2119 SemiPro Controller. Controller with 2 knobs the back knob is for brake control.

[RichD]

A bigger picture would be helpful, to me that looks more like the old diode based controller, but I am not certain of that. If it is diode based the control is for variable brakes and it could be a 2044 or 2045. The 2044 had alligator clips and the 2045 had a phono plug. If it is a transistorized model with only one knob that would be for the sensitivity adjustment.