The 410PT from Cossor is a battery output pentode. This valve design was obsolete by 1933 and not listed in the 1935 Cossor catalogue. The audio output was 0.9 Watt.
Seen from the top and side of the envelope the wire grids are clearly visible. The inner grids pass flat across the filament and are therefore parallel with the anode walls. The outer suppressor grid is an open spiral close to the anode.
The balloon envelope is 45 mm in diameter, and excluding the B5 base pins is 89 mm tall.
References: 4010 & 1043. Type 410PT was first introduced in 1932.
Absolute Maximum Operating Conditions¶
Updated April 11, 2013. shape:balloon construction:pinch type:pentode age:1930.1940 base:b5 heater:4.0v pins:5 pin: