The 3CX100A5 or 7289 is a 100 watt, air cooled, planar triode with a mu of 100 and full rating frequency of 3000 MHz. In 1957 Eimac data, the 3CX100A5 was a premium 2C39B with a 6.3 volt filament, but by 1958, the filament was given as 6 volts. The 7289 replaced the 2C39 tubes but would required an adjustment in the filament voltage. Some early 3CX100A5 tubes had the numbers engraved in the anode and different grid rings. Various versions like the Y262 in the fourth example were made for special applications. The 3CX100F5 (8250) is the same tube with a 26.5 volt, .2 to .24 amp filament. For pulse service, the ceramic insulators were lengthened and the 7815R family of tubes were produced.
Length = 2.70" Diameter = 1.25"
Max voltage = 1000
Max current = 100 ma
Fil voltage = 6
Fil current = .90 to 1.05 amp