The 4-250A or 5D22 is a 250 watt dissipation tetrode. The usable frequency for maximum ratings is 110 MHz. This tube started development in early 1944 and ending about 1946 after about 42 experimental prototypes. The first tubes had fins similar to the WWII 250TH/TL tubes as shown with the experimental tube in the second example. Penta Labs produced tubes only designated 5D22 and GE produced tubes with the GL-4-250A marking. The fifth example was made by Amperex and the sixth was made by RCA and has both designations. A version of the 4-250A had MYKROY base insulation instead of white ceramic. It is unknown if this was an experiment or a production tube. The 4F21 is the same tube in Japan.
Length = 6.38" Diameter = 3.56"
Max voltage = 4000
Max current = 350 ma
Fil voltage = 5
Fil current = 14.5 amps