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Hey, let me try again. I need to know if anyone can tell me what type of noise filter to use on my '72 SS Tach. THis is a filter that mounts on the firewall and goes between the negative lead of the coil and the tach. Mine lost a lead and I need to know what to use. Ground up says they are discontinued. This an autotrans car with A/C.

Thanks
 

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Try MSD, they make a noise filter that can be used for several differant jobs.

[This message has been edited by Dragn70 (edited 01-14-2001).]
 

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Is there something different about a 72 from a 70. I have a stock tach in my '70 and it has no filter of any kind between the coil and the tach. I have also run the tach off the tach terminal from an HEI unit and it was fine.

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Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)
 

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Is the noise filter to cancel noise heared on the radio? I've never heared of a tach creating that kind of noise, however there are two kinds of noise interference found in a car. The first is a popping usually caused by plugs & wires (resistor plugs & wires help to eliminate this)the noise filter to get rid of this is a capacitor between the positive lead & ground. A capacitor "passes" high frequency sounds and blocks low frequency ones (such as popping, frequency is determined by the amount of cycles per second) popping is very low so the noise is bled off to ground. Second, a high pitched whinning is caused by the alternator charging circuit, this type of noise is stopped with an RF choke, basically a coil of wire with one led in & one out. These pass low frequency sounds (DC voltage has no cycles per second or zero frequency)but block high frequency sounds. Hope this helps & wasn't too confusing. The same technology is used in speaker crossovers to separate the highs & lows & send them to their appropriate speakers. A combination of the two will get rid of all the noise.

Good Luck
 
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