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BTH Audion Box - Why the French R Valve?
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British Thomson-Huston started making soft valves in 1916 with the Audion seen here. During WWI governments has paused the patent litigation surrounding valves as the demands of the war were such that the best possible communications were required.
Soft valves of the day were more sensitive than the hard valves but unstable and required a skilled operator to maintain the correct gas pressure during operation. BTH spent much time in developing the Audion to try and make a stable and reliable valve. They succeeded in improving the original Audion but ran into serious difficulties in 1917. The next step was a soft valve based on the French TM valve and designated the R2. This was produced by several companies.
The stability required for military operation was found by using the hard valve in spite of the lack of sensitivity and the need for multistage amplifiers. Thus the R Type became dominant and the inconsistent performance of soft valves resulted in their discontinuance.
Thanks to David Tayler for sending the images of both the valve and the box.
The twin anode plates and grid iron grids are supported from one end of the bulb and the filament is fixed into the lower pinch and connects to the base.
The filament has four lengths between the grid and anode but most of the grid and anode is outside the electron flow.
The BTH logo is etched into the glass on this side and other details appear on the other. Note the horse hair wadding that protected the delicate valve during transit.
Patent number, serial number and filament volts etched into the glass.
Another view of the faint etched lettering.
The BTH logo.
The anodes are spot welded to their supports at each of the corners nearest the pinch. The grid wire is held in only one place.
The balloon envelope is 50  mm in diameter, and including the candelabra base is 80 mm tall.
Reference: 1047. Type Audion was first introduced in 1911. See also 1911 adverts.


Absolute Maximum Operating Conditions
Updated September 28, 2016.
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