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The SP4B from Mullard is a short grid base (straight) indirectly heated HF pentode with a second application at LF. The heater voltage is the then standard UK value of four Volts.

The B7 base cap and pins.

Thanks to Mark Mallison for sending the images.

The classic envelope is  mm in diameter, and excluding the B7 base pins is  mm tall.

References: Data-sheet, Data & ¹⁰⁴³. Type SP4B was first introduced in 1935. See also 1935 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.