Marconi "Osram"

A Marconi "Osram" R5^v bright emitter triode.

Electrode structure and the 1922-24 BBC mark.

The M.O. Valve Co.'s "Osram" trademark.

R5^v box

The original
R5^v leaflet

This is a Marconi "Osram" type R5^v bright emitter triode. The R5^v is an improved version of the 'R'-type. This example was made after the introduction of stamp regulations on Nov 1st., 1922, but before September, 1924, when this particular style of mark was withdrawn. It was made at the M.O. Valve Co.'s Osram Lamp Works, Brook Green, Hammersmith, London.

The anode is a flattened oval and the grid is an oval spiral wound on a sturdy 'J' shaped support. The filament, in the form of an inverted 'V', provides an increased length and, presumaby, an increased area of emission, compared to a traditional 'R'-type. It has a sprung top support to eliminate filament sag.

The original leaflet claims that these improvements increased filament life, reduced microphonics, improved uniformity and reduced HT requirements by 25%.

It has a tapered tubular balloon envelope with a top seal. The base is a nickel plated Marconi pattern B4 base with petal pins. The contact wires are soldered near the top of each pin. The bulb is half silvered with a Magnesium getter.

The characteristics given, which show a 50% increase in gain over the standard 'R'-type, are:-

Filament Voltage

5.0 V

Filament Current

0.7 A

Anode Voltage

30 V - 120 V (45 V normal)

Amplification Factor

9

Anode Impedance

30,000 Ω