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This Osram valve is marked 'Wireless Receiving' No. R2. The candelabra cap is present together with the connecting wires. Our other R 2 has clearer etched lettering but no candelabra base..

These are a rare and unusual specimens of British-made replacements for the de Forest audion. The R2 was still a soft valve as the hard valves lacked the sensitivity required. The R2A of the box above would differ from the R2 only in the composition of the low pressure gas filling.

This Type R2 has nothing to do with the later rectifier.

Audions, and the British-made replacements, were 'soft' (i.e. gas-filled) valves and had to be operated at low anode voltage (typically around 20 V). In Britain such valves were used almost exclusively by the Navy, who went on doing so long after the other Services had moved on to using hard valves. It is interesting to note that even the earliest type (the R2) is clearly a derivative of the French TM valve which became the Type R design not made in Britain until 1916. Moreover, the Navy continued to develop and improve these soft valves. Later types, including the R2A and R2B, were externally similar to the R2 and R5 but had different gas fillings. The erratic characteristics of the soft valve paved the way for the universal adoption of the hard valve in spite of needing multiple stages to achieve the same gain.

The triode construction is standard for the period, with a single filament strand passing through the centre of the anode cylinder, the grid is a wire helix surrounding the filament and supported both ends.

The etched lettering is, Valve Wireless Receiving, No. R2 and Pattern 3987.

Enhancing the image makes the lettering clearer.

The main supports are of twisted wire and the electrodes are fixed to the supports with folded sections.

The folded grid supports on the right.

Face on the grid helix can be seen to be secured with a fine twisted wire.

The remains of the single strand filament.

The join of the envelope with the pinch stem showing the twisted lead-out wires including one filament wire passing through a loose glass tube.

The candelabra base with one wire passing through an insulator to the central connection and the other soldered to the outer brass screw.

Under the microscope - not so clear this end.

Here the fine wire securing the grid helix to the internal rod support is much clearer. The remains of the filament being held in the fold of the support is in the foreground.

The balloon envelope is 51 mm in diameter and, excluding the base pins, is 82 mm tall.

Reference: ¹⁰⁰³.