diode rectifiers. GE subsequently upgraded 22 of the units (a few at a time) to an E44a designation, boasting upgraded traction motors and silicon rectifier packages for an output of 5,000 horsepower. The 22 E44a's were numbered ; the E44a program was terminated in 1970 due to the Penn Central bankruptcy. Conrail subsequently swapped out the Ignitrons in all of the remaining units for silicon diodes in the late 1970s and early 1980s, in-house and without any horsepower upgrades. In 1980, GE took E44a 4453 in hand for rebuilding with upgraded electronics and uprating to 6,000 horsepower. Made redundant by Conrail's discontinuance of electrified freight operations, the rebuilt 4453 was briefly tested on the Northeast Corridor in 1984 by GE, which then scrapped the unit several years later after salvaging the newer components. In the late 1960s, General Electric constructed two upgraded 5,000 horsepower (25,000 volt, 60 cycle) units of the same E44 body style (known as E50Cs) for the Muskingum Electric Railroad, a private coal-carrying railroad owned by American Electric Power. Until it closed in 2002, MERR shuttled coal in two automated consists from the mine to a powerplant at Relief, Ohio (across from Beverly, OH). History Pennsylvania Railroad The Pennsylvania took delivery of 66 E44s between 1960–63 and they quickly displaced the P5s. The Pennsylvania used the E44s on just about any freight assignment imaginable, on all of its electrified lines. They could work both singly or lashed together as multiple units. They quickly proved to be very versatile and could handle just about any train, without helpers. The E44's dynamic braking, a novelty under PRR wires, made them just as sure-footed descending grades as climbing them (although the brakes were not regenerative). They even occasionally hauled passenger trains in emergencies, although they were not very adept in this role, being (officially) limited to , having a pronounced oscillating tendency at speed on jointed rail, and of course lacking steam generators for passenger service. The units were delivered in an entirely new paint scheme. While adorned in the familiar PRR Brunswick Green, the units carried the sans-serif road name in yellow, flanked by two small PRR keystones, together with a keystone on the front and rear, and a large yellow road number. This scheme was unique to the E44; all subsequent diesel orders omitted the road name. The impact of the lettering was diminished by the fact that