4CX250F
The 4CX250F is a beam power tube designed to operate up to 500 MHz with plate voltage up to 2000 V. It was originally designed as an RF power amplifier tube for transmitters and requires forced air cooling. The 4CX250F is used in the sweep circuit of the 519.
The 4CX250F is the same as the 4CX250B, but with a 26.5 V filament instead of a 6 V filament.