The 2C39A or 3X100A5 is a 100 watt, planar triode with a full rating frequency of 2.5 GHz and a mu of 100. The 2C39A replaced the 2C38 and 2C39. About 1958 there was supposed to be a small difference between the 2C39A and the 3X100A5, which was described as a premium tube, but this later disappeared. The 2C39B is the same tube with a ceramic body in the early Eimac tubes where it replaced the glass 2C39A and later transitioned into the 3CX100A5 (7289) about 1958. In the 1960s, Eimac was still making the 2C39A and B tubes, but they were now all ceramic insulated and the 3X100A5 designation was dropped. Other varients are the rugedized 2C39WA and 2C39XA. The 2C39WA tubes made by Eimac had 6.3 volt filaments and Machlett tubes had 6 volt, 1 amp filaments, but the operating range for the WA was 4.5 to 6.3 volts so they should be interchangeable. Sylvania specified 5.8 +/- 5%. The RCA 2C39WA/C is the sixth example and is a WA with ceramic insulators. The seventh example is the 2C39AM (ML-2C39AM) and the eighth is a 2C39M (ML-2C39M). The 6897 is a similar tube.
Length = 2.75" Diameter = 1.27"
Max voltage = 1000
Max current = 125 ma
Fil voltage = 6.3
Fil current = .90 to 1.05 amp