The 4-400A or 8438 is a 400 watt dissipation tetrode. The usable frequency for maximum ratings is 110 MHz. 4-400As were made with several different plate configurations by Eimac. The fifth and sixth examples were made by Eimac and Penta with just the 8438 (PL-8438) marking. The seventh example was made by Amperex which is also marked with the European number QB4/1100GA. The 5F23 is the same tube in Japan. The last photo is a pair of 4-400As "on the pump" courtesy of Lane Upton.
Length = 6.38" Diameter = 3.56"
Max voltage = 4000
Max current = 350 ma
Fil voltage = 5
Fil current = 14.5 amps