General Electric constructed the first 60 E44s (4400-4459) using Ignitron rectifiers, and the final six units (4460-4465) with air-cooled silicon 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, who then scrapped the unit several years later after salvaging the newer components.