The 4E27A or 5-125B is a 125 watt dissipation pentode. The usable frequency for maximum ratings is 75 MHz. The first example is an RCA with a ceramic pin support disk in the base with a cooling hole in the middle. The second tube, an Eimac, is basically all glass and open on the bottom. The aluminum skirt around the pins is only for air flow control. The third example was made by Sylvania with similar construction to the newer Eimac.
Length = 6.18" Diameter = 2.75"
Max voltage = 4000
Max current = 200 ma
Fil voltage = 5
Fil current = 7.5 amps