The DP-Pen is an indirectly heated mains output pentode. It has the unusual heater rating of 16 Volts at 0.25 Amp. It was introduced in 1933 in both B5 and side terminal and B7 base caps. The DP-Pen was obsolete by 1935.
The following is taken from the 1935 Cossor Valve Manual.
For operating moving coil loud speakers, the Cossor DP-Pen is supreme among mains indirectly heated DC Pentodes. It is capable of delivering big, undistorted volume with perfect quality. When occasion arises for using this valve with moving iron loud speakers, a tone corrector should be employed, which is true of any pentode, whether battery or mains operated. The heaters are, of course, intended to be wired in series with a suitable dropping resistance, so that the current passing through the heater is 0.25 Amps.
The optimum load is given as 10,000 Ohms. The grid wires follow the shape of the anode as can be senn below.
The balloon envelope is 48 mm in diameter and, excluding the B7 base pins, is 93 mm tall.
References: Datasheet, 4010 & 1043. Type DP-Pen was first introduced in 1933.
Absolute Maximum Operating Conditions¶
Updated December14, 2012.