The 10LD3 is a double signal diode triode with a common cathode. This configuration was typical of valves designed for superhet receivers. The diodes would be used to demodulate an AM signal and also to develop an AGC voltage to control the gain of the IF amplifiers and possible the RF amplifier if fitted. The triode would function as a voltage amplifier for the demodulated audio signal.

The thin glass envelope is 20 mm in diameter and, excluding the B8A base pins, is 53 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 10LD3 was first introduced^¶ in 1953.

 
Pin Connections

B8A	1	2	3	4	5	6	7	8
	h	a	g1	s	a(d2)	a(d1)	k	h

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	13.0	0.1	100	-0.7	0.8	54k	1.4

Thanks to Frank Philipse for supplying the above PDF datasheet