Thanks folks that gets me started.

I began to think the B suffix I got from the US manual is a red herring as the description of the unit from that manual matches AndyY’s description.

However taking the image from vacb’s post I checked with my “Air Ministry Catalogue Serial No 1 Issue 1 April 1942” (which I got from Australia and was led to believe to be a localised version of a similar UK one) I see it matches what that catalogue calls a “10A/261 Socket type 108” but which actually on the illustration is marked as 10H/261B which explains why looking in the index didn’t get me there. So now I know what I’ve got to find thanks.

All very confusing with my starting point being a circuit diagram in a US manual!

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