The 2C39 or GL572 is a 25 watt, planar triode with a full rating frequency of 500 MHz and a mu of 100. GE developed these tubes in the mid 1940s as shown in the first example (GL-2C39). The early Eimac tubes (also designated 3X100A11) have different grid connections and the third tube appears to be the earliest as the second is physically the same as the early 2C39A it replaced. The fourth example was made by Machlett (ML-2C39). The Eimac tubes have removable radiators.
Length = 2.75" Diameter = 1.27"
Max voltage = 1000
Max current = 125 ma
Fil voltage = 6.3
Fil current = .90 to 1.05 amp