Cossor Types P1 and P2 were tungsten-filament 'brights', like the R Type and were not gettered. Early samples were fitted with shiny metal base caps; the red (bakelite?) type dates from around 1924.

Cossor did later make thoriated versions of these types but these were designated the P3 and P4, had larger and more bulbous envelopes, and were gettered.

The unique feature of the P1 and P2 (which looked identical except that one had its top dipped in red paint) was that the filament was self-sprung in the form of a semi-circular bow, following the 'hooded' form of the anode. The grid also followed the same hooded shape. This arrangement not only avoided the need of a filament tensioning spring but also side-stepped patents covering the 'French' construction arrangement used in the Type R and many other early 'brights'.

The anode is a flattened parabolic hood with a bright finish. The control grid is a series of wire loops attached to a flattened metal ring, seen under the anode hood.

The wide glass tube envelope is 27 mm in diameter and, excluding the base pins, is 78 mm tall. The B4 base is 31 mm in diameter.

 
Pin Connections

B4	1	2	3	4
	a	g1	f	f

 
Absolute Maximum Operating Conditions

Triode	Ah
	0.75

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This exhibit was last updated on 22 October 2008