Prototype set is here

[miniman82]

After following some wires from the CRT socket, it quickly became apparent that there are 3 tubes (6BL7's) that are driving pins 3, 8 and 18 on the CRT socket (which would be grids on a 15GP22). I assume that means these are the adders or some part of the matrix, but the strange thing is there are also 3 diodes on terminal strips for each one as well. They look like the same type of thing that always seems to get used as a detector in IF strips. DC resto, perhaps?