The Y-266 is a 250 watt, forced air cooled, power tetrode with a full rating frequency of 500 MHz. This is a ruggedized varient of the 4CX250B with transverse cooling fins and a mounting flange. It was made for Westinghouse circa July 1961. The first example has a flat flange and the designation printed on the flange. The second example has rivnuts for mounting and the designation moved to the upper cooling fin.
Length = 2.38" Diameter = 1.85"
Max voltage = 2000
Max current = 250 ma
Fil voltage = 6
Fil current = 2.6 amps