The A520 general purpose triode is unusual in that the heater runs at full mains voltage. It was made in two versions, one for 200-220 Volts for Europe and a second type for use in America with 110 Volt mains. It is reported that 4 metres of 0.015 mm tungsten wire are used in the heater. The valves were designated for AC or DC mains and our exhibit says DC and not for sale.
Ostar Ganz, located in Vienna, made valves from 1932 until the late 1930's. The UK importer was Eugen Forbat.
The electrodes are mounted horizontally and the anode is made of wire mesh. The screening is provided by an external wire cage. The wire appears to be iron.
A view of one end of the heater, cathode and control grid. The anode has side flanges and the support struts pass inbetween the two layers of mesh.
The grid is supported by a support passing through the anode. The external screen can be seen to have oxidised.
The anode top view.
In this view of the electrodes the grid can be seen to have a thick support one side and a thinner longitudinal support the other side. The cathode tube has an oxide coating within the anode mesh.
Looking through the anode. The electrode supports can be seen shaped and held in the pinch.
The base has the connections marked on it.
The balloon envelope is 50 mm in diameter, and excluding the B4 base pins is 91 mm tall.
References: 1043 & 3002. Type A520 was first introduced in 1932.