Thanks, Allen, and no problem. It’s a very interesting topic, but not one that has been subject to much in-depth treatment in the railfan press. In a general sense, the impression I have is that the complexity and cost of heterogeneous MU has been such that railroads have used it sparingly and only where its was justified by regular, or at least reasonably recurring operational needs. I agree that in the VGN case, it looks as if EL-C plus EL-2B combinations would not normally have been needed, so if the facility was there, it might only have been used in abnormal situations.
Still, if it was done, I’d be interested to know the “how” details, particularly in respect of matching the regenerative brake control of the EL-2B to the dynamic brake control of the EL-C. I don’t know how regeneration on the EL-2B was controlled, but in referring to motor-generator locomotives generally, it was sometimes possible to exercise control both through the regenerative exciter (brake handle) and the main generator excitation (throttle/power handle).
The information that I have on hand about EL-C power control indicates that, like the New Haven EP-5, it had a limited number (5 in this case) transformer tappings, beyond that using resistance control to provide the requisite number of accelerating notches. But the resistance grids, also used for dynamic braking, were force-cooled, so may have been suitable for continuous operation, apparently unlike the EP-5 case . The EL-C also had a buck-boost transformer system to provide three sub-notches for each accelerating notch. But as an “auxiliary” function, that would not necessarily have had to be replicated on all potential MU partners.