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.
Through the internal coating the electrode system can be seen.
Side view of the anode.
A closer view of the internal structure. The control grid is wound on copper supports and has radiating fins above the top mica. G3 is internally connected to the cathode.
The classic envelope is 44 mm in diameter, and excluding the UX6 base pins is 102 mm tall.
References: Data-sheet & 1040. Type 18 was first introduced in 1937. See also1937 adverts.
