The CV1438 is a design from WWII. It is an audio output beam tetrode and with a power output of 4.3W was suited to low power public address systems etc.

After WWII when designs for television receivers were being published in journals such as Wireless World, the EL33 was used as a line timebase output valve. In such service the EHT supply was derived from a transformer and not via the line timebase. The CRT sizes employed were 9 and 12 inch. The HT voltage was up to 420 Volts.

The classic envelope is 42 mm in diameter and, excluding the IO base pins, is 120 mm tall.

References: Datasheet & ¹⁰⁴⁰.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	g2	g1	-	h	k

 
Absolute Maximum Operating Conditions^¶

Beam Tetrode	Vh	Ah	Va	Vs	Vg	mAa	mAs	gm	Pout	D
	6.3	0.95	250	250	-4.4	40	8.5	10.5	4.3W	8%

Thanks to Frank Philipse for supplying the above PDF datasheet