Note that the wire colors used in your sets may not match the colors shown in the schematics or in my adaptors. The diagrams below show RMA color codes and the adaptors that I use with my Universal Shop Speaker. Zenith and some other manufacturers used the RMA plug wiring but different wire colors. They also specified wire color codes for two other arrangements but without specified plugs, one with six wires including a tapped field coild and one with seven wires including two field coils. In November, 1936, the RMA (Radio Manufacturers' Association) published standards for plug connctions and color codes for three arrangements using four-pin plugs and one using a five-pin plug. Part One - RMA Standard Speaker and Field Coil The alligator clip leads are colored or tagged tagged to match their banana plugs (see the bottom part of this photograph).
Note that I had only red and black test lead wire (extremely flexible and rated for high voltage) available, so those colors are shown in the plug and cable diagrams, and the plug colors match the jacks used on the Universal Shop Speaker and Dummy Field Coil in my shop. The sockets and plugs are shown from the pin ends of the plugs and the inside of the chassis, and the pin numbers are the same as those for tube bases. I use capped speaker plugs that mate with 4-, 5-, 6-, and 7-pin tube sockets (see the top part of this photograph showing some of them), but if you don't have those you can use bases from dead tubes for your plugs. Here are some common cables using easily available plugs bases upon tube bases. My universal shop speaker can be used with almost any electrodynamic speaker chassis by using a set of alligator-clip cables, but it is easier to use a cable with a plug to match the speaker socket. Star City Antique Radios - Speaker Plugs and Field Coilsįor the Universal Shop Speaker and Dummy Field Coil
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