We believe this to be an AR Type. Only Ediswan used the 'safety cap' of shorter filament pins (introduced in 1923). The envelope has no makers information only the words 'Repaired By Radions Ltd'. Clearly a repaired triode but sadly the filament has burned out. In repairing this valve Radions used phosphorus gettering, and this imparts the golden colour to the inside of the glass.
The AR is a bright emitter receiving triode. The AR stands for Amateur Radio. 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 safety cap. At a time when valve bases did not have recessed sockets it was quite easy to connect the filament across the HT battery and instantly ruin an expensive valve. The Ediswan solution was the shorter filament pins that could only make contact after the valve was correctly inserted in to the holder. Later moulded valve holders with recessed sockets made the precaution obsolete. The P denotes the Plate or anode pin.
The safety cap. The main pins are 17mm long with the filament pins 13 & 9mm respectively. The wires from the pinch are soldered to the top of the simple split pins.
The tungsten wire filament is held in place by compression of the supports. The rest of the fixings are spot welded.
The helical grid is fixed to the twin support rods by a thin wire wound round the turns. The support rods are in fact a single rod bent over at the top.
Another view if the grid fixing method and the broken filament.
The wide glass tube envelope is 28 mm in diameter, and excluding the B4 base pins is 87 mm tall.
References: 1004 & 1003. Type AR was first introduced in 1922. See also1922 adverts.
