The FC13C is an octode frequency changer. It was made in two versions, the FC13 on a Ct8 base and this version on a B7 base.
In use the local oscillator would be formed between the cathode and rods in the g2 position. Two screen grids are present at g3 and g5 with a suppressor grid as g6. The signal being added at g4, the top cap.
This valve is marked as Made in Holland - Philips. Our other FC13C has a slimmer envelope.
The reverse is plain metal paint - coloured gold.
The B7 base pins show no sign of use.
The classic envelope is 48 mm in diameter and, excluding the B7 base pins, is 117 mm tall.
References: Datasheet & 1043. Type FC13C was first introduced in 1935.