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Discussion Starter · #1 ·
I have been trying to find a replacement coil. Every one that I have looked at (including the GM Delco replacement from the chevy dealer) are stamped "use with external resistor only". The guy at the chevy dealership said "that is the correct replacement according to the book". Are all new coils designed to be used with external resistors or should I keep looking?

Dwayne
 

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So.... what are you using it on? All Chevrolets, with the exception of HEI, use an external resistor. Either a resistor wire, as in A bodies or a block style resistor used on older cars. Coils will have internal resistance, that's how they work, but use an external resistor to prevent overloading the windings.

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Dave Bradley
www.corvetteforum.net/classics/d1_bradley
'69 SS396 ragtop
'33 3W Coupe
'65 Vette BB Roadster
 

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Discussion Starter · #3 ·
OK, so let me guess, the small chrome round thing about the size of my thumb mounted inside the distributor with a wire that connects to the points...that is considered an external resistor? Boy do I feel stupid.
 

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No, that's a capacitor. Also called a condensor. The external resistor is built into the wire that goes to + coil. Wire has a cloth-like cover on it. It's not like a normal wire, more like a wire that's used inside a toaster.
 

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Discussion Starter · #5 ·
<BLOCKQUOTE>quote:</font><HR>Originally posted by John_Muha:
No, that's a capacitor. Also called a condensor. The external resistor is built into the wire that goes to + coil. Wire has a cloth-like cover on it. It's not like a normal wire, more like a wire that's used inside a toaster. <HR></BLOCKQUOTE>

Hey, I've got that wire....now I really feel stupid..

Dwayne
 

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Just hook it up. Youll be fine. The condensor...it's really a capacitor as stated above by John, is used to shunt the high frequency pulses to ground while blocking the DC so it won't short out. It's for noise supression and to save the points a little bit. You might also have one off of the coil.

Chuck
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by New68SS:
Hey, I've got that wire....now I really feel stupid..

Dwayne

<HR></BLOCKQUOTE>

Why feel stupid? Nobody here knows all the answers. 100 people probably read what you wrote and said "I never knew that."
 

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The external resistor is there to step down the voltage applied to your coil. Coil operating voltage is in the neighborhood of 8 to 9 volts as I recall. (anybody correct me if I am too far off here) Your system is 12 volts and the engineers have determined that 12 volts is too much for the coil in your car, or rather too much for the points in your ignition system. So they step the voltage down a bit. Even after stepping the voltage down there are still voltage spikes induced when your breaker points open. Hence the condenser in your distributor.

Why don't they simply rewind the coil for less voltage you ask? Well if they did that and reduced the size of the coil then there might not be enough secondary voltage to properly fire your spark plugs under ALL engine operating conditions.

If your condenser fails in the "open" mode then your points will quickly burn up because the voltage spikes that it normally soaks up are going across the points. If it fails in the "closed" or grounded condition then your car stops running. As chuck B said the condenser normally blocks DC current. If the condenser fails to ground then it takes all of the DC current that would create voltage in the secondary portion of your coil and shorts it to ground. Then you get to walk.

anyway I gotta get to work. Have fun all.
 
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