PX4

Initially mainly used in battery sets, it was later widely used in mains equipment and amplifiers. It went through several stages of development over 3 decades from the starting date of 1929 and is found in balloon, ST and straight envelopes.

The early versions had a maximum anode rating of 200 volts and 40mA with a filament current of 0.6A. The bulbs of these were blackened by the azide process used for the filaments.

Some rare balloon versions from the first three years of manufacture also exist with angled structures. These were favoured for use in telephone repeater amplifiers where the angled structure was thought to prolong the life of the tube.

From about 1933 as it became used less in battery sets, the anode rating was increased to 300 volts and 50mA enabling a 3.5W power output instead of the 1W of the 1929 version; the filament current being increased to 1A to accommodate this increased power. The transconductance quoted was raised from 5mA/V to 6mA/V.

PX4: GEC's catalogue supplement Anonym 413 Sammler
PX4: Telefunken Werkstattbuch Wolfgang Bauer	Just Qvigstad	PX4: osram wireless guide 1931 Giuseppe Antonio Tusini Mehr...

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