ID:
521
Maker's Name:
Philips
Where made:
Other
Dimensions:
5.3 × 5.3 × 10 cm
This is an early tetrode valve, sold for Amateur Radio use. Manufactured in the 1920s, it has a bright emitter filament ie pure Tungsten, operating at 3.5 Volts. An anode voltage of up to 80 Volts could be used, so this valve has a hard vacuum.
With a coarse self-supported helical control grid and screen grid, this was not a sensitive valve, having a Gm of 0.8 mA per Volt (800 uS), and a maximum plate current less than 10mA.
Book reference:
Tyne, Saga of the Vacuum Tube
