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The S23 is a directly heated tetrode. The valve has a high impedance and would be suited to tuned anode circuits at HF or IF. Probably used in straight TRF receivers. It is an early tetrode. The grids can clearly be seen in the picture, the anode appears to be a pair of rods outside the screen grid. This is possible given the low current rating of the device.

This exhibit is a good example of the improved type of construction made possible by the change from Azide to oxide processing. Note particularly the way in which the electrode assembly is firmly and accurately held together by machine-punched mica supports above and below. Not only did this greatly reduce microphony due to the lack of rigidity of the clumsy support system required by the Azide process but, equally important, it enabled much closer grid-filament spacing to be used, thus increasing the gm value, the gain, and the gain-bandwidth product 'at a stroke'.

Moreover, it was much easier than the old method to assemble on a mechanised production line. This was faster, cheaper, more accurate and, above all, cleaner, than the old methods. Cleaner valves need less baking whilst on the pumps, and last longer in service. Perfecting the somewhat tricky oxide coating process cost M-OV a considerable investment in time, money, and factory reorganisation but it paid back handsomely. The sometimes painful change-over to oxide processing during the early 1930s was the starting point of M-OV's golden age in the later 1930s when they wrested UK market leadership from Mazda.

The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 115 mm tall.

References: Data-sheet & ¹⁰⁴³. Type S23 was first introduced in 1933. See also 1933 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.