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The Type 18 is an audio output pentode. The anode dissipation is 11 Watts, the load impedance should be 7,000 Ω and the cathode bias resistor 410 Ω.

Under these conditions an audio power output of 3.2 Watts is to be expected.

The pinch and lower mica can be seen by looking up under the coating.

The dome with mica sheets tightly fitting the shoulder on the glass envelope. The control grid is fitted with heat dissipating fins.

The classic envelope is 44 mm in diameter, and excluding the UX6 base pins is 104 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type 18 was first introduced in 1937. See also 1937 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.