The 15E is a miniature UHF power triode designed by Eimac (the Eitel-McCullough company of San Bruno California USA) in 1940 for use as an oscillator in the first American airborne radar, the ASB search radar. The matching rectifier is the 15R. Both types feature a directly heated thoriated tungsten filament. The 15E operated at 5.5 Volts.
Both devices are high voltage types designed for low duty cycle pulse operation at up to 600 MHz. The maximum anode dissipation is given as 20 Watts
The 15E was designed for a maximum anode voltage of 15,000 Volts when used as a pulse modulator or 12,500 Volts when used in RF service. In both cases the maximum grid voltage was 10,000 Volts.
The ASB-1 transmitter operated with with two EIMAC 15E triodes operating as a blocking oscillator at 515 MHz. Pulses of 2μS duration were generated at a repetition rate of 400 Hz. The peak pulse power was 5 kW but the average RF power was 4 Watts. The energy of each pulse was 0.01 Joules.
The later ASB-3 employed four 15E triodes also in a self quenched oscillator (blocking oscillator) to produce 10 kW pulses.
The final type ABS-7 used six 15E's in a ring oscillator circuit. The valves had to be closely matched for this circuit.
See also the PDF file attached to exhibit 1S/3iII.
The The anchor and letters US for the American Navy printed on the glass. Also etched into the glass is the Eimac trade name and Type.
The grid and anode connections seem to pass through uranium glass.
The cylinder anode connected to the side connection and the control grid secured to the top cap connection.
The green tint that indicates a uranium glass seal. The cage grid has a helical wire traversing the grid length. The thoriated tungsten filament is fixed to the centre support and then is formed into a helix that passes down to the base connection.
A close-up of the central section.
The wide glass tube envelope is 35 mm in diameter, and excluding the base pins is 57 mm tall.
References: 3002 & Internet. Type 15E was first introduced in 1940.