[DaleHCook]

The speaker plug is a D shaped plug made of 3 layers of phenolic material. It actually has 4 pins but it only uses 3 of the pins.

That plug should have one small pin and three large pins. I have seen no definitive pin numbering, so unplug the speaker cable, and look at the speaker socket from outside the back of the chassis. The pin numbering which I have adopted for that socket as seen from the outside is:

[Image: https://plymouthcolony.net/starcity/radi...co-rev.jpg]

Pin 1 is the small pin. Now let's figure out which speaker leads do what. First, which pin is not used? Leave the speaker unplugged for easy access to the socket pins. By any chance do you have 4-pin and 6-pin tube socket adapters (aka socket extenders)? They would make this easy, but I suspect that many, perhaps most, collectors do not own a set of tube socket adapters.