Summary

Expanse double filament triode. Sold by Amalgamated Wireless in Australia. Forerunner of Expanse B type electronic valve, made 1921-1923.
Bright emitter 'soft' triode for use as a detector. 6 to 8 V directly heated cathode

This valve is almost certainly an Audiotron manufactured by E. T. Cunningham.
In an agreement signed between E.T. Cunningham and RCA in June 1920, RCA gave Cunningham a licence to produce up to 5000 valves for up to 90 days. They were to be permanently marked 'For amateur and experimental use only' but Cunningham only used paper labels to which RCA objected. He then introduced etched labels. The 90 days was later extended to October 1920. A second agreement between RCA and Cunningham made at the same time provided that when the 90 day period had expired, Cunningham would cease manufacturing valves and would henceforth market valves made by RCA but branded Cunningham.
In view of the close relationship between RCA and AWA it is possible to speculate that at the end of the extended 90 day period, Cunningham still had stocks of his Audiotrons and it may have been suggested that they could disposed of by sending them to far away Australia so that Cunningham could concentrate on marketing RCA's line of valves which he did at the end of 1920.
AWA did not start manufacturing Expanse B valves until early 1921.

Physical Description

Tubular glass bulb with a pinch at each end. 3 wire leads at one and two wire leads and the exhaust tip at the other.

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