Valves from before WWII

Here is a timeline of the development of valve manufacture in the U.K. up to 1930.

The very first valve

A large early rectifier

Triode valves from the dawn of Broadcasting 1920-25

Data for these valves was apparently not published but I have found some heater data which may be of use to those wishing to "light up" one of these valves. There is a characteristic curve on the B5 page.

Battery Triodes from 1925-40

Mullard

Philips had invented the 'Azide' process which increased the emission of dull emitter cathodes beyond that obtainable from thoriated tungsten. This process produced an oxide covered cathode which was more robust and long lasting than other competing methods, for example the A.C. Cossor 'Wuncell' type. Before assembly the tungsten filament was directly oxidised or plated with copper and oxidised. The anode was coated with barium nitride (Azide). After evacuation the anode was heated (probably by induction) and the evaporated barium nitride reduced the oxide on the filament forming barium oxide, metallic tungsten or copper and nitrogen which was adsorbed by the getter.

Mullard commenced production of these P.M. (Philips Mullard) valves in 1925 with the PM3 and PM4.

Other Makers

The PX230 and PX4 have quite heavy filament currents and although directly heated they are often used in mains equipment.

Battery Rectifier, Tetrodes, Pentode and others

A 2 volt full wave rectifier for battery eliminators and directly heated tetrodes for battery powered superhets and RF amplifiers etc. The QP21 is a double pentode for quiescent push-pull (Class B) audio amplification.

Mains Valves

Valves for use in mains powered receivers etc. Mostly indirectly heated, with 4 volt 1 amp heaters. The S130 is a cold cathode voltage regulator.