The AR from Ediswan is a bright emitter receiving triode. The AR stands for Amateur Radio.
The main picture shows that etched into the envelope is the BBC stamp with the words 'Type Approved by Postmaster General' This stamp was used from 1st November 1922 until September 1924 and thus we can date this exhibit to between these dates. The AR design originated in 1922 and was a development of the R Type, the μ was given as 10. Ediswan were among the first manufacturers of the R Type in Britain and the AR shows the way that valve technology developed. The anode became a vertical cylinder and the filament became supported on a sprung support to maintain filament tension when hot.
The red paint line declares that this is the HF version of the AR. In total three variants were produced with the green and red introduced in 1925. This conflicts with the date that the type one BBC stamp was in use. The best we can conclude that this is a very early red variant. The plain glass envelope denoted the general purpose type and the green stripe identified the detector/AF amplifier version. The stripe versions had a higher mutual conductance than the original that had a mutual conductance of 0.17 mA/V. Also it is generally accepted that the variants had the evacuation seal at the bottom, and so this also suggests that this exhibit is from one of the first batches.
See also The ARDE which is the dull emitter replacement for the AR valve. Additionally Ediswan introduced the AR.06 dull emitter triode in 1923. The latter having a 3 volt filament running at 0.07 Amps.
The wide glass tube envelope is 30 mm in diameter, and excluding the B4 base pins is 91 mm tall.
References: 1004 & 1003. Type AR was first introduced in 1922.
Absolute Maximum Operating Conditions¶
Updated August 07, 2019. shape:wide.glass.tube construction:pinch type:triode age:1920.1930 base:b4 heater:4.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f