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3 wires on power cord ??

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3 wires on power cord ?? Empty 3 wires on power cord ??

Post by bill57 on Sun Jun 28, 2009 5:24 pm

OK, B. Cahill, I'll try a radio post here as I sure would like this forum to keep going. I purchased a Motorola model 67XM 21 and the power cord on it has three wires. Two of them are together on one leg of the plug. On the schematic it shows one of these going to fm ant. and one side going on to 50B5 tube. The other single wire goes to the on/off switch. I have not seen this before in my long 2 years of working on radios. Is this third wire a line resistor I have read about. This original cord is completely shot so I need to replace. Can I put on a standard cord? Any advice appreciated.

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Post by Tony V on Sun Jun 28, 2009 11:45 pm

You answered your own question. The extra wire is for the "built in" fm antenna. It is not a line cord. Just hook the neutral side of the cord to the 50B5 and the hot side of the cord to the on/off switch. The 3rd or antenna wire, just leave it off the power cord and get a 5 ft length piece of wire and hook it to your FM antenna connection on the back of the radio. Those built in line cord antenna set ups were never safe if the 50mfd cap ever failed thats in circuit shown on the schematic. They didnt work that great either. Motorola was the main one for using this three wire set up. They even used the same cord on their wireless record changers with the antenna wire used to transmit instead of recieve like in your radio.
-Tony
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Post by Bill Cahill on Mon Jun 29, 2009 5:42 pm

Thanks, Tony. Yes, that's right. The third wire is merely antenna wire, and, stays disconnected.
You can add another 20' of wire for better reception. Don't ground the chassis, either......
I have a Motorola am oscilator I rescued out of a junk Motorola that had a 78 turntable. All the pot metal parts had dis-intergrated, so, I only saved the two tube oscilator.
The 6J5 is the rectifier, and, the 6SA7 is the oscilator tube.
I added a matching transformer so I could connect it to an amplifier for better sound.
It had that 3 wire cord, and, the one wire was the antenna.....
At one time I had a longer wire on it so I could get better reception in the house.
I tried it last year, and, it still works, but, otherwise, haven't used it in over 20 years....
They're fun to play with, though....
Bill Cahill

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Post by bill57 on Mon Jun 29, 2009 9:14 pm

Thanks guys, Learn something every day in this hobby. I just thought it was strange going to the FM. Next time I see one I'll know.

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