The DF33 is a variable μ RF pentode for dry battery operation. Mullard designate this device for service at both RF and IF in broadcast receivers. It was part of the 'red series' of valves that were first introduced in 1938.

The relatively large size of the valve suggests that it was not designed for battery portable sets but for fixed operation. The filaments had to have the lowest possible consumption due to the cost of the dry batteries.

We also have the DF33 with a metal skirt between the IO base and the envelope.

The wide glass tube envelope is 28 mm diameter and 81 mm long excluding the IO base pins.

References: Datasheet, ³⁰⁰² & ¹⁰⁴⁰. Type DF33 was first introduced^¶ in 1939.

 
Pin Connections

IO	1	2	3	4	5	6	7	8	tc
	m	f+	a	g2	-	-	f-	-	g1

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	1.4	0.05	90	90	0	1.2	0.3	1.5M	0.75

Thanks to Frank Philipse for supplying the above PDF datasheet

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