<VV> Tachometers

[Padgett]

>Smitty says:  Some time back, someone made a post about converting a
>tachometer to work on 4-6-8 cylinders, I believe by changing a resistor.
>Anyone remember the post or the particulars of it??

With reference to GM transistor and parasitic d'Arsonoval tachs (pretty 
much all from 1960 to 1973), it is a capacitor that is changed. 33 ufd for 
a 8, .47 ufd for a 6 & .68 ufd for a 4 (plus some minor trimming).

For more than you ever wanted to know get a copy of AC-Delco Service 
Bulletin 3D-5 (mine is dated Dec 1, 1978 superceeding issue of October 1968.

The entire bulletin is 27 pages so if I scan it to a .pdf
1) it will take quite a while
2) be somewhere around 25 MB.
3) probably would need permission from GM to make available (is a way, just 
a bit complicated).

Basic parasitic circuit (and heart of transistor circuit) is just an RLC 
bridge with some diode steering and a zener to clamp voltages.

Padgett