The AP412P is an output bi-grid valve and was made in 1927 for the unidyne circuit. Aneloy as a company started trading in 1926 as a repairer and a re-seller of other valves such as those made by Thorpe and/or Philips. The 1927 range of bi-grid valves they made themselves at their premises at Dulwich in London. The advantage of the space charge grid bi-grid was short lived as conventional triode design improved.
The oval anode is small in cross section and bright. The semicircular supports are for the filament.
The anode in close-up. The outer grid is clearly seen but no so the inner grid. All that can be seen is a flattened cylinder. It is assumed that the inner grid is shorter than the outer grid.
The support seen at the lower part of the image holds the top of the filament. The folded top wire of one filament strand can be seen on the left of the anode. The filament was clearly two vertical strands.
Looking upwards through the bulb the folded anode and its support are visible.
At no angle of view was the second grid visible.
The balloon envelope is 46 mm in diameter, and excluding the B4 base pins is 96 mm tall.
References: 1043. Type AP412P was first introduced in 1927. See also1927 adverts.
