The PX25 is one of the all time classic audio output triodes. This example is branded as a Marconi product as can be seen below, note also the hand construction with the band held against the pinch.

The PX25 is an early audio power triode, and was one of the first to give a significant output. 26 Watts to the loudspeakers of the time 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.

Today PX25 is much sought after by collectors, and New Old Stock (NOS) valves in their original packaging sell for over £100.00 each. This exhibit was £40.00 in 2003.

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.

MOV redesigned and uprated the PX25 over its 30-year production life, so that it was fit for service in more demanding applications including RF.

The balloon envelope has a maximum diameter of 60 mm and excluding the B4 base pins it is 137 mm tall.

 
Pin Connections

B4	1	2	3	4
	a	g	f	f

 
Absolute Maximum Operating Conditions

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

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 03 June 2007 {find valves by name}