The EBL21 is one of very few double diode audio output pentode valves that were designed.

The valve has a common cathode and the diodes are for signal rectification for detector or AGC service. As an example of both use and date, this valve type was used in the 1947 Philips 462A radio for detection and audio output. It would have needed considerable drive at the intermediate frequency and the output pentode is of high gain to allow the use a a single stage from detector to output transformer.

Mullard describe the EBL21 as a high sensitivity output pentode, combined with twin diodes, for use in AC mains operated equipment.

The wide glass tube envelope is 32 mm in diameter and, excluding the B8B base pins, is 76 mm tall.

 
Pin Connections

B8B	1	2	3	4	5	6	7	8
	h	a	g1	g2	a(d2)	a(d1)	k	h

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout	D
	6.3	0.8	250	275	-6.2	44	5.8	50K	9.5	5.5	10%

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 02 December 2007 {find valves by name}