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MG TD TF 1500 - Judson Electronic Magneto Info

Does anyone know much about these? I heard or read that the 12v neg ground cars may need a ballast - actually I think the Judson Instr say that. Does
anyone have any idea where one buys that and what to ask for?
Keith NJ
K E MURPHY

Keith,
Got a volt/ohm meter?
Measure the resistance. Ballast is essentially a resistor used to lower the resistance and just about any auto parts store will have one if you need it.
(IF you don't have a meter take the coil with you ...Jeggs for sure should have)
Somebody jump in here...been a while and my manual is across the street in the garage...I believe you are looking for a resistance of 3.5 ohms?
Pretty sure you will only need a ballast if you coil was made for a 6 or 8 cylinder application.
Cheers,
David 55 TF1500 #7427
David Sheward

I hate to disagree with you Dave but a ballast resistor is used to raise the resistance of the coil/ballast to a number that won't draw too much current through the points (or electronic device). In the day,the Ford ballasts changed resistance as they heated up. So that a full spark was obtained at 3 volts input( starter drawing gobbs of current to turn the engine over when it's cold). Then as the ballast heated up it's resistance would rise to hold the current to close to the same value as the voltage rose to 7.3 or so as the generator got to work. Thats one of the reasons the early Ford V8's had such a good reputation before the war.

Some of the wiring systems were rigged to go around the ballast while the starter was being used to be sure there was a good spark to get the engine started. Don't remember if the Fords did that though.

I think pertronix recommends a minimum of 3.5 ohms for the coil (12V system). If your coil is less than that, then you should put a ballast in series with the coil. One thought is that a light bulb changes resistance as it heats up. Two 21 candle power bulbs in parallel would be about right to be a ballast for coils in the 1-2 ohm region.

Just my $0.02 worth.
Cheers

Bob
R. K. Jeffers

Keith, I had one, You will need a resistor, I believe I used a Mopar ballast resistor.Check OEM coil voltage to the points, then recheck w/ the Judson.
Len Fanelli

Bob is right of course ...raise the resistance.. lowers the ohm-age is how I should have worded that.
Thanks for catching that.
Cheers,
David


David Sheward

This thread was discussed between 29/07/2009 and 04/08/2009

MG TD TF 1500 index

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