This may help explain why.
(This issue was raised in part on another post this morning.)
I ran some informal tests this morning, using an inexpensive analog voltmeter and reading it as best I could. Except as noted, I measured the transformer outputs (“hot” post to common) without any load. The numbers are the minimum volts that the device could put out before dropping to zero.
Postwar ZW 250 A = 7.5, B = 7.2, C = 7.0, D = 7.0
Postwar ZW 275 A = 7.5, B = 7.5, C = 7.4, D = 7.3
Postwar KW A = 7.2, B = 7.2
Postwar 1032 A = 5, B = approx 1
Postwar 1033 A = 5, B = approx 1
Marx #329 A = 6.2
CW-80* (1) A = approx 1
CW-80* (2) A = approx 1
Above these minimums, the throttles would all increase relatively smoothly, although the precision of the resulting incremental speed increases varied from one transformer to another. (The ZW’s were a tad coarser than the CW-80s, for example.) These results should be no surprise to anyone who has ever looked inside a postwar transformer, most of which do not put anything out less than 5 volts, at best.
These tests were conducted with the transformers operating a zero load, except for the CW-80’s* which were powering 2 small yard lamps in order to read sensibly.
The significance is that my sole Williams diesel, for example, unmodified from the way it was manufactured, could run smoothly and nicely, pulling 3 freight cars and an illuminated caboose, at realistic scale speeds. Similarly (once warmed up) my venerable old 2332 GG1 from 1948 gave comparable results. (She is one stately old lady!)
Neither, however could approach the kinds of low speed, non-stalling performance of some of the fancy electronic throttle systems that I’ve seen; but they wouldn’t go flying off the ping-pong table either.
Coupling/uncoupling operations could be carried out without doing any damage. The