Stewart Warner Tach to HEI Distributor

I picked up a vintage Stewart Warner Tach Model number 997RS6. It seems new in the box. I hooked it up to a Chevy 350 with the HEI distributor. Green wire to the Tach connection on the distributor, red wire to the power source and black wire to a ground on the battery. The darn thing won't read the signal from the distributor. The needle moves slightly when it's powered up but it won't register the RPMs.I know that it is getting a good power source and the ground is fine. I also hooked up another tach to see if the signal source in the Distributor was good. It was.
I think that the tach dates back to 1959 and wonder if that has anything to do with it. The Steward Warner tech guy in Canada hadn't seen this tach and couldn't find anything on the internet. Any help would be greatly appreciated. Thanks

A tachometer circuit is fairly simple in that it converts frequency to current to drive the meter. It is made up of a handful of resistors, capacitors, diodes, a bridge rectifier and perhaps a transistor (or two). In all likelihood, this tach was designed to operate with points and condenser and will not work without a filter to address the high frequency interference generated by the HEI.

This part should fix the problem (assuming the tach has not been damaged):

New Vintage USA 99004-04 - New Vintage USA Tachometer Signal Filters - Overview - SummitRacing.com

If your attached to this tach, it may be worth a try if you want to part with $33 plus the handling charge.

Good Luck,
Glenn

Thanks for your response. I was wondering if it needed a filter to handle the HEI. I think that I will pick up a new tach from Summit next time that I'm down there.
Great site, Thanks again