The VR40 is the PX25 (PP5/400) in military uniform.

This early audio power triode was one of the first to give a significant output. Five Watts single ended and up to 20 Watts in push pull. With the loudspeakers of the time this was suitable to fill a small hall. With transformers of the period being less efficient than later designs an audio power amplifier using a pair of these valves was a substantial piece of equipment, and heavy.

The ratings given are for class AB1 push pull for a pair of such valves. Under these conditions the grids would require 108 Volts peak to peak to achieve full output.

The balloon envelope has a maximum diameter of 60 mm and excluding the B4 base pins it is 133 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³.

 
Pin Connections

B4	1	2	3	4
	a	g1	f	f

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah	Va	Vg	mAa	Pdiss	D
	4.0	2.0	500	-54	82	26	4%

Thanks to Frank Philipse for supplying the above PDF datasheet