Arkless Electronics
Trade: Amp design and repairs.
This shows the topside of the L15 decoder board. Annoyingly, I don't have a photo of the track side, nor a diagram! Wish I had. However I think it was essentially what was on the TI datasheets.
http://jcgl.orpheusweb.co.uk/temp/L15pic.jpeg
I can't recall when, but I think some 600s used some soft 'plastic washers' that took the place of mica insulators + heatsink compound. The idea being that they were soft enough to act as both. The were opaque. But I have no idea how they might have aged over this many decades!
The same MPX filter appears to have been used again then but it's a completely different board to the RCA decoder equipped one.
I'll have to give the OPT mounting a proper once over when I do the rest...