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Mazda were rightly proud of their AC operated valve pentodes and made their status plain in the name AC/S2Pen. This exhibit has external metalisation and the later top-hat form of top cap. ACS2/Pen has the older style of screw top cap.

The AC/S2Pen would be used in the final RF or IF stage of a radio or early TV, immediately before the detector stage where the signal strength fluctuates and can sometimes be quite high (tens of volts). For the 1930s the gm was respectable at 4.6.

The valve is also suitable as a high-gain audio amplifier capable of providing the relatively large signal voltages required at the grid of a PX4 type triode output stage.

The Mazda ACS2/Pen a great improvement on its screen-grid predecessor (AC/S2) but was in turn soon overtaken by classic video pentodes such as the EF50 which not only had higher gm and better gain-bandwidth product but was more compact, easier to make, and less power-hungry.

The AC/S2Pen, then, was a fairly short-lived valve linking 'wireless' technology to the new imperatives imposed by high-gain video amplification.

The reverse is plain zinc paint.

The balloon envelope is 45 mm in diameter and, excluding the B7 base pins, is 106 mm tall.

References: Data-sheet & ¹⁰⁴³. Type AC/S2Pen was first introduced in 1933. See also 1933 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

PDF scanned from an original document held by the museum