The PX4 is one of the classic audio power triode valves. This exhibit represents the final (300V, 15W) post-war design.

The PX4 is directly heated triode in the classic shape. The filament is a single wire formed vertically within the anode cavity into four inverted V's. The grid is a single wire formed between two vertical notched rods 1.5 mm in diameter. The grid zig-zags around the filament.

This valve was also produced in a balloon envelope.

The balloon had a maximum diameter of 56 mm and excluding the base pins, is 123 mm tall.

When used in class AB1 push-pull a pair of PX4's would deliver 13 Watts.

LP4 a PX4 relabelled as a Ferranti Type LP4, represents the penultimate design stage in which the (previously 12 watt) rating has been up rated to 15W by tacking carbonised fins onto a shiny anode. There were about 8 definable stages of redesign and uprating between the original azide-process PX4 of 1928 and the classic Hi-Fi valve shown here.

The electrode system is only about 5 mm from front to back, but is 30 mm wide and 45 mm high.

The classic envelope is 48 mm in diameter and, excluding the B4 base pins, is 120 mm tall.

 
Pin Connections

B4	1	2	3	4
	a	g	f	f

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm	Pout	D
	4.0	1.0	300	-50	50	830	6.0	4.5	4%

Thanks to Frank Philipse for supplying the above datasheet

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This exhibit was last updated on 02 December 2007 {find valves by name}