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Base UX4

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This is the American four pin bayonet base. It was introduced in 1926 and replaced the short pin UV base.

The pins count clockwise from the left hand large pin. The locating pip is mounted between pins two and three. Typically the filament/heater connects to the two larger pins.

The pin-outs below refer to the data researched by Keith R Thrower OBE.

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