AA5 power cord

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Post by Ben Delk on Tue Apr 03, 2012 2:18 pm

I'm a computer geek by trade so my world exists in ones and zero, + and -, 3 wire grounded circuits. These AA5 with a so called hot chassis admittly confuse my thinking. If iI replace the power cable with a polarized one, wide blade is neutral, narrow blade is hot, is it possible to have the power filter (multi-section cap) polairty reversed? I lean to the cautous side with electrical, my work surface is high density rubber, I stand on a rubber mate I use an iso tranf and variac. I don't worry to much about touching things I shouldn't but more about where and how to actually check voltages with dmm or analog. I'm thinking if Underwriters Labs was in business in the 30's and 40's we would have fewer radios. To say the least a chaasis with 115 volts across it and earth ground makes me scratch my head. Anyone have a tried and proven way to go about checking line voltage.
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Post by Resistance is Futile on Tue Apr 03, 2012 2:42 pm

Yes it is possible to have the capacitor polarity reversed. The Power caps are always on the DC side.
Testing the line voltage is simple on an AA5.

Put one probe on the volume control switch (incoming Hot side) and the other on the chassis with the switch in the off position (of course you can have it on also using your probes.) It may also be wired up with what they call a floating ground rather than to the chassis, so you have to take into consideration the voltage drop when turned on.
Of course when the set is off the voltage will be at line voltage with no drop, as no current is flowing.

note: sometimes they are wired incorectly and the chassis is hot all the time hence a shock hazard.
Some radios also have a dropping resistor built into the power line cord, it would only be with cloth covered wire though.

You don't hook up the ground and neutral to a common tie point. You can use a polarized plug but don't connect the ground wire in the power cord to the radio.
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Post by Ben Delk on Tue Apr 03, 2012 9:48 pm

Well gentlemen you were correct. When I replaced the old multi cap with the 3 single caps, I did indeed reverse the 50 cap lead. I corrected that error and music now comes out of the speaker quite abundantly. I have a little static but now I can go back and check the resistors to see if I created any issues there. I have purchased lots of equipment for testing but the one thing I need to purchase is new glasses. Dumb mistake but that is a lesson I will not forget. Thanks again for the re-direction and I'll update you when it is ready to set up on the shelf.

Many Blessings,
Ben
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Post by Bill Cahill on Wed Apr 04, 2012 12:27 am

Could also be a dirty tube socket, tube pins, or, a noisy tube.
Glad to help.
I will be moving this to radio rpeairs, since it is about repairing one.
Bill Cahill

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Post by Resistance is Futile on Wed Apr 04, 2012 3:46 am

Just knowing we helped, is like accomplishing the task on my work bench. Gives us all more confidence. Cool
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AA5 power cord Empty Confused n these AA5

Post by W8WHO on Tue Apr 17, 2012 9:43 pm

Hello to All. While on this topic of AA5 Polarity I still get confused. What is the best way to make these radios safe? If I put a polarity cord on correct I also see they sometimes have a cap to the hot side of the AC to ground chassis. Also I have purchased these new safety and interference caps and will install those. Sometimes I still get a small AC voltage of around 12-20v from chasses to another ground.
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Post by Ben Delk on Wed Apr 18, 2012 5:25 pm

Here's an article I found on it but must admit I have not tried it yet.

http://www.geojohn.org/Radios/MyRadios/Safety.html
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Post by Sinatra1982 on Wed Dec 14, 2016 9:16 am

I have a German radio Emud Record Junior 196 with a resistor cord which is rubber. The cord is bad and I don't know how to hook up a new cord because of the third wire. Any information on how to to do this?

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Post by Bill Cahill on Thu Dec 15, 2016 11:12 am

I believe the resistance wire is wound around the other two wires.

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