There was a time, before there were the modern conversions for our
tachs, that some folks in TE/AE (I believe one involved was Tom Ehrhart)
made measurements on the accuracy of our "state of the art"
transistorized tachs and found that they were quite questionable. This
indicates that the normal deterioration of the old electronics in the
tach is the main cause of the inaccuracy, not anything to do with the
use of Pertronix ignitions. IIRC, you can often rehab an old tach by
replacing the big capacitor on the circuit board or, if that failed,
replacing the transistors which could be found very cheaply at Radio
Shack. However, nowadays it is a Good Idea to convert to Pertronix or
some other more reliable ignition system in our cars, for obvious
reasons. You can also replace the coil with a new Pertronix and do away
with the ballast resistor at the same time. It also makes sense to me
to have the old electronics in the tach replaced with a new circuit
board. Tom Hall and Theo Smit have designed such an improvement and can
make the conversion for you. It cost me $165 a couple of years ago and
I expect the calibration will outlive me. If you want to preserve the
original tach for posterity, pack it up and put it away and use
another. Most of the Smiths tachs are interchangeable as the mechanical
parts are pretty standard. If you add a new circuit board, it can be
calibrated for your setup. I am using a tach out of a Series IV Alpine
with the new circuit board installed. The lettering is identical to the
stock MkI/IA tach except for the notation (in small letters) that
indicates "4 cyl, positive earth" which hardly anyone can read,
especially Jim Armstrong. It has the added benefit of having a higher
red line. Use the tach out of a Series V Alpine if you have a MkII
Tiger. You can even have the face redone with new lettering by Paul
Breuhan if you wish, so no one will be the wiser.
Tod
B382002384LRXFE
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