The CV3991 (4X150D) has a heater rated at 26 Volts for working off of 24 Volt vehicle supplies. The 4X150A differs only in having a 6.3 Volt heater.
The 4CX150D beam tetrode is a close relative to the 4CX250B VHF/UHF RF power output valve and has the same finned anode structure. The silver plated fins are contained in an outer ring, and in use air would be forced over the fins for anode cooling. A special base and chimney were designed for the purpose.
The spigot connects to the control grid g1 the base ring to the screen grid g2 and the finned top section (radiator) to the anode.
The base is a glass disc with pins protruding through. The evacuation seal is covered by a central metal spigot.
The the military identification arrow and what looks like a date of April 1962 - the correct period.
The RCA name and Type designation on the anode.
The the base spigot with key for collect alignment in the valve holder. Looking through the glass the anode can be seen to be copper. Outside it is silver plated.
The co-axial glass envelope is 33 mm in diameter and, excluding the B8F base pins, is 46 mm tall.
Reference: Data-sheet. Type CV3991 was first introduced in 1954. See also1954 adverts.
