Models: D18S and D18C, No. 9         Issued: September 9, 1946 Reprinted:  September 25, 1950 Revised:  June 1, 1953 REVERSE CURRENT RELAYS AND VOLTAGE REGULATORS In order to give better efficiency in the maintenance of the reverse current relays and voltage regulators, located in the control panel box, this service letter lists below several […]