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The American Government specification VT-233 is a double diode triode sharing a common cathode and the commercial Type designation is 6SR7. The 'S' indicates that it is a single ended valve ie no top cap. The ratings are the same as the older 6R7 - with a top cap.

This triple sectioned valve was designed for superhet AM receivers. The first diode acts as signal detector feeding the audio signal via a volume control into the triode AF amplifier before the signal passes to the audio output valve. The second diode produces a DC voltage that is directly proportional to the audio signal and this voltage is used to control the gain of IF and RF stages of the receiver.

Compared to the pin compatible 6SQ7 this valve would exhibit lower gain in the triode stage.

The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 50 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type VT-233 was first introduced in 1940. See also 1940 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.