Will i need a tach adapter for the mallory CDI 6 a box? or just the blk/prpl wire to the yellow wire on the box?

Depends if the tach out signal from the mallory works with the tach, some later tachs will work, hook it up and see. I think the early tachs wanted a 12v signal, and the cd boxes output 5v or vice versa.

Mine wouldn't work with the mallory VI-AL, tried everything. It was the day before my race so I ran out to my FLAPS and they had this low-line Autometer tach. Works perfect and fits directly in the stock hole.

I may try and take the guts out of the autometer and put them in the stock VDO, wanted to keep that "vintage" look.

I've got a schematic here somewhere for a circuit that will convert the 5V signal to a 60V pulse to drive the early tachs. (And late too, but the late tachs run on 12V or higher pulses so might work as they are).

Anyone want the schematic? Or I could build up tested circuits if a few people want them.

QUOTE (Otmar @ Dec 24 2004, 11:16 AM)

I've got a schematic here somewhere for a circuit that will convert the 5V signal to a 60V pulse to drive the early tachs. (And late too, but the late tachs run on 12V or higher pulses so might work as they are). Anyone want the schematic? Or I could build up tested circuits if a few people want them.

si senor!

i want to use my stock tach with the box....

mallory booklet

QUOTE

..This output produces a 12v square wave.....

Is this for the 73?
My 73 works fine with a 12V square wave.
If it's for the 70 then you'll need a adaptor.

I couldn't get my '73 to work from my mallory VI-AL. Tried the tach lead, the coil lead, and the dizzy lead.

Also tried another known good tach.

Even though i don't like the way that Autometer looks, it sure works great. No bounce, float, just smooth.

Ummm, foot in mouth time...
Now that I think of it, I think my 914 is actually a 74.
Sorry for the bad info...

So maybe they changed the tach input in 74? I'm really not sure.
I guess I should look into making an pulse adaptor and seeing how they work.

QUOTE (Otmar @ Dec 24 2004, 12:52 PM)

Ummm, foot in mouth time... Now that I think of it, I think my 914 is actually a 74. Sorry for the bad info... So maybe they changed the tach input in 74? I'm really not sure. I guess I should look into making an pulse adaptor and seeing how they work.

well....my car is really a 74.... i put the early gauges in it....seems to work fine....

so....what will i need to complete this beasty

QUOTE (Aaron Cox @ Dec 24 2004, 12:53 PM)

so....what will i need to complete this beasty

I've pulled up the ascii art schematic and put it here: Tach Driver

If you're into minor electronics, you could build one from that I think. Stan claims that it worked for him.

This comes up every now and then so I'm also thinking of building a few to sell. Of course I want to change the design since I am an engineer at heart.

If someone has a tach that does not work on the 12V pulses, I'd like to borrow it to test the design. Mine doesn't help since it does work on the low voltage pulses.

QUOTE (Otmar @ Dec 26 2004, 03:52 PM)

I've pulled up the ascii art schematic and put it here: Tach Driver

Do we have an "over my head" smilie?

i can handle that....

but...my gauges arte glass face early ones....

At this point I have no idea anymore which ones need the high voltage spike and which ones don't.

I would just hook it up directly and if that does not work then add the circuit to boost the pulse.