The 4CX300A is a VHF power tetrode with an external anode that is 41 mm in diameter and designed for forced air cooling within a special base and chimney. The maximum frequency of operation at full ratings is 175 MHz and with 1,500 Volts on the anode the 4CX300A can deliver 250 Watts of RF when operated as Class C.
The 4CX300A can also be used in a pair as a Class B audio power amplifier or modulator.
The construction is co-axial and exhibit QV1-150A shows the concentric arrangement of the electrodes. The grids are aligned for minimum screen current.
The large surface area around the anode of this forced air cooled valve.
The anode radiator and the connecting strips. The valve would be pushed into the holder and twisted to lock.
The hazard sheet that came in the box of this new old stock valve.
Thanks to Mark Mallison for sending the images.
The ceramic tube envelope is 29 mm in diameter, and including the base is 60 mm tall.
Reference: Datasheet. Type 4CX300A was first introduced in 1956.