The W31 is a variable-μ RF pentode on a B7 base and designed for use on a 300 mA series heater chain in universal (AC and DC) mains sets.

The W31 is pin compatible with the Catkin W30 but has a higher specification.

Looking under the extensive silver gettering the only clear detail is of the heater entering the round cathode tube, The cathode is fixed to a lower screen.

The classic envelope is 44 mm in diameter, and excluding the B7 base pins is 119 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type W31 was first introduced in 1935. See also 1935 adverts.

Pin Connections

B7

1

2

3

4

5

6

7

tc

m

g1

g3

h

h

k

g2

a