6 volt to 12v help

1931 flamingo

1931 flamingo

Well-known member
Picked up a period correct (new) tach for the 40. Car is 6v pos ground.


What have others done (a link to part would be nice) to "make" 12 volts negative??



Any input would be appreciated.
Paul in CT
 
I don't remember who, but thought someone here on the barn sold such a device. I know Old Henry was messing around with these type of arrangements for some of the devices he added to his car. Believe part of it was a 6v to 12v transformer, but don't remember how the handled the polarity. Might search some of his post. The polarity shouldn't be too big an issue as long as everything is isolated (no common ground with the vehicle).

Do you have a wiring diagram for the tach? The tach trigger signal could be an issue, not sure.

Ok, it is tubman (that's what I thought, but my memory is not always the best! :)) https://www.jalopyjournal.com/forum...tachometer-on-6-volt-positive-ground.1066826/
 
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Try tubman. He's into elect. stuff and sharp as a tac....pun intended. I have an old Ford 12v tach that i 4got about. I think i may be interested too. mike
 
Mike is correct. My partner and I have developed just the device you are looking for. It allows you to use most any 12 volt negative ground tachometer on a 6 volt positive ground vehicle. This was not a simple task. We have sold out our first production run and are taking orders for a second run. The price is $120 plus $7.20 shipping. If there is enough interest, we will make another run. Here is a video of one running on an engine on my test stand : https://www.youtube.com/watch?v=TaxpuDkWAqc. It shows the engine at rest, then starting. It then pans down to the unit itself, and ends by showing the 6 volt Optima battery used on the test engine.
 
I hope no one minds me resurecting this thread. I am getting to ready to tach up my 1940 for the Spring. I have a quote for a restored Sun 90 degree readout, 4K RPM, red football tach converted to one piece and to operate on 6-V +ground for $550. I like the look and the dual pointers on the Sun.
I see new 12-volt, 270 degree readout, 4K RPM tachs that paired with Tubman's converter would likely total less than $400.
Tubman, what's the current purchase status of your converter?
I know that tachs like everything else are highly personal, but do any of you have experience with any of the units out there? Reliability and accuracy?
Thank you.
 
I just had my 40 rewired (Brig's Rod Shop, Wolcott, CT, GREAT folks).
He wired up my 12V tach to the 6V and it works but registers 1/2peed. Great because it's more for looks than practicality. Used all original harnesses, hooked up the signal lights and also got the wipers working. MIKE was just great.
Paul in CT
 
Are you sure you have the tachometer set to 8 cylinders? The tach works by counting pulses from the ignition; that it works at all on 6 volts is kind of a miracle. Most tachs have settings for 4-6-8 cylinders. Yours has all the symptoms of being set for 4 cylinders.

If it is set incorrectly and starts working correctly when set to 8, please let us know what kind it is; it will be a boon to the 6 volt guys.
 
FireEngineMike said:
I hope no one minds me resurecting this thread. I am getting to ready to tach up my 1940 for the Spring. I have a quote for a restored Sun 90 degree readout, 4K RPM, red football tach converted to one piece and to operate on 6-V +ground for $550. I like the look and the dual pointers on the Sun.
I see new 12-volt, 270 degree readout, 4K RPM tachs that paired with Tubman's converter would likely total less than $400.
Tubman, what's the current purchase status of your converter?
I know that tachs like everything else are highly personal, but do any of you have experience with any of the units out there? Reliability and accuracy?
Thank you.
Click to expand...

I may have one or two of my tach driver boxes left; I'll have to check. The initial 10 I produced sold quickly, the second 10 not so much, so I gave up on them. All of them that are in use are still working properly as far as I know. You may not even need one depending on what we find out from what's going on in the last two posts.

I don't think a 4K tach is enough for a flathead, even a stock one. If you want to use a 12 volt tach that looks like a classic SUN, check these out : https://www.amazon.com/gp/product/B00UM9X87Q/?tag=atomicindus08-20.
 
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When I converted the 41 to 12V, I wanted to run a period tach. I had an early 40's SW tach that was presentable but unrepairable.

I removed the internals and replaced it with a mechanism from a modern 12V tach. The conversion was fairly straightforward.

It's not super accurate, but it looks good (and I shift by ear anyway).
IMG-4735.jpg
 
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