The 4-1000A or 8166 is a 1000 watt dissipation tetrode. The usable frequency for maximum ratings is 110 MHz. It replaced the 4-750A by April 1947 when its tentative data was released. Early Eimac tubes like the second example had Chrome metal base skirts. RCA tubes as in the third example, had ceramic base insulators. The fourth example was made by GE (GL 4-1000A) and the fifth was made by Penta (PL-8166/4-1000A). A varient of the 4-1000A is the Y-364.
Length = 9.63" Diameter = 5.25"
Max voltage = 6000
Max current = 700 ma
Fil voltage = 7.5
Fil current = 21 amps