FL9AC rebuilds and disposition

Thanks for the explanation, Dutch.

So there weren't any problems with the 12-710, I take it?

Sounds like they should've used traditional DC traction systems, and perhaps these units would still be on the road today.

There was no way to put a DC propulsion system of over 3000 Hp in same locomotive and keep it a Dual Mode.
DC traction motors of the size needed would not even fit in the Fl-9 trucks.

Worth noting that it's not unheard of to use one inverter to control two motors - I think EMD does it today on their ACe series and it's done in crane applications all day long. That said, the FL9AC program was almost 30 years ago when inverters were a black art rather than a science. I've heard horror stories about Thor inverters from 1990-ish. We actually used thyristors or static stepless in cranes when it non-contactor control was called for.

One problem in railroading is wheel sets do not wear equally so motors will not run synchronous, max size difference on passenger locomotive with Siemens drive is 1/4 of inch.
On GE system there is no limitation as each traction motor has its own inverter.

There was no way to put a DC propulsion system of over 3000 Hp in same locomotive and keep it a Dual Mode.
DC traction motors of the size needed would not even fit in the Fl-9 trucks.

I don't think that's true at all. The front Flexicoil B on the FL9 has the same general dimensions as a Blomberg B truck, a design that has been used on modern units with up to 4000 hp - and in fact, many 3000 hp GP40-2's of the 1970s rode on old Blomberg trucks from traded-in F-units. The rear truck of the FL9 was a Flexicoil C, a design used (with brake and component upgrades) right up to Conrail's SD50's of the 1980s.

Also - the AC traction motors on EMD's 70MAC and GE's AC series are both larger than the DC motors on the DC 70 and Dash-9. Unless the FL9AC motors were significantly smaller, they already require more clearance than newer DC motors to begin with.