07-14-2016, 11:28 PM
I am replacing the transformer on a speaker for a Philco model 70 which uses a single 47 output tube. I have the transformer. The supplied speaker is from a Model 20. I also have the Philco schematic. My question is this: I know that the two wires, from the transformer are for the voice coil. I also know that there are two terminals used on one side of the transformer and that is the primary. Opposite the two primary terminals are two which are unused. I know that they are for use as tie points for the speaker connecting cable. Here is the situation. I also need to put on a new speaker cable. From the schematic for the Model 70 it looks like I should only have three wires to the speaker plug. I suspect that one of the primary terminals goes directly to the speaker cable to connect to the 47 plate. The other secondary connects to one side of the voice coil and to another speaker cable lead which goes to supply point "C" B+ for the radio. The other field coil lead goes to point "D", which is connected to the bleeder resistor. I can easily trace the correct speaker plug connections from the chassis. However is there a correct and an incorrect way to wire the speaker field coil? While I am very experienced with radios, field coils are almost a new thing for me! Thank you.