The type 26 audio triode is a directly heated AC triode for audio amplification. This exhibit was made by National Union.

Turned through 180 degrees, the construction can be seen as the silver gettering does not obscure all of the envelope. The box anode is much wider than it is front to back.

The anode seen from the underneath. The wire grid and the single inverted V oxide coated ribbon filament can be seen.

The top of the envelope. The hairpin bend of the ribbon filament is held in the tension spring.

In greater close-up it can be seen that some of the oxide has fallen off of the top of the right hand side of the filament.

The classic envelope is 45 mm in diameter, and excluding the UX4 base pins is 102 mm tall.

References: Datasheet & ³⁰⁰². Type 26 was first introduced^¶ in 1927.

 
Pin Connections

UX4	1	2	3	4
	f	a	g1	f

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	1.5	1.05	180	-14.5	6.2	7,300	8.3

Thanks to Frank Philipse for supplying the above PDF datasheet

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