The ARP35 is the UK Army, pre-WWII, name for the EF50. It is clearly a utility valve with its plain aluminium screening can devoid of the familiar red point.

The valve is a high impedance variable μ pentode and was a workhorse of receivers for TV, radio and especially war-time radar.

The wide glass tube envelope is 32 mm in diameter and, excluding the B9G base pins, is 60 mm tall.

References: Datasheet & ¹⁰⁴³.

 
Pin Connections

B9G	1	2	3	4	5	6	7	8	9
	h	g2	a	g3	s	k	g1	s	h

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.3	250	250	-2	10	3	1M	6.5

Thanks to Frank Philipse for supplying the above PDF datasheet

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