the "Air Throttle MU" was a Westinghouse product.
its advantages were Infinite Throttle Settings.
but it had a big disadvantage,only 3 or 4 units could
be reliably controlled by it.Electric MU was good for over
8 units if needed.
Baldwin was the main user,but it could be found on some
F-M units,Lima units,and maybe the Ingalls unit that used
Westinghouse supplied parts.
Baldwin did offer Electric MU as an option,Erie units had
Electric MU.
Spikre