Snap-On MT640 Coil Tester

[Conaway2]

I just acquired one of these - no user directions came with it, other than what’s printed on the unit itself.

It looks like it’s designed to test a coil installed in the car….

I would appreciate any guidance on how to hook this thing up.

Many thanks - Jim

[alexiskai]

I did a video on it:
https://youtu.be/2X6LPS2zgUw

[Conaway2]

Originally Posted by alexiskai

I did a video on it:
https://youtu.be/2X6LPS2zgUw

Thanks ! Great video - explains everything.

Jim

[Conaway2]

Originally Posted by alexiskai

I did a video on it:
https://youtu.be/2X6LPS2zgUw

Thanks ! Great video - explains everything.

Jim

[Gene F]

I am guessing that they no longer make these.

[alexiskai]

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Originally Posted by Gene F

I am guessing that they no longer make these.

Correct, they’re usually found on eBay

[shew01]

The one I bought on eBay is missing the little neon(?) tube between the electrodes. Does anyone know what that thing is called or where I might find a replacement?


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[alexiskai]

Those tubes are called Geissler tubes. No one makes them anymore, but if you search online for "discharge ampoule," you can find some tubes filled with chlorine, bromine, or iodine gas that are pretty similar and might fit the MT-640.

[shew01]

Originally Posted by alexiskai

Those tubes are called Geissler tubes. No one makes them anymore, but if you search online for "discharge ampoule," you can find some tubes filled with chlorine, bromine, or iodine gas that are pretty similar and might fit the MT-640.

Thanks!


Sent from my iPhone using Tapatalk

[katy]

Will a neon bulb work there?

[alexiskai]

Originally Posted by katy

Will a neon bulb work there?

Probably. The tester works just fine with the tube missing. It comes into play when you have a really bad coil or condenser; the tube should light up when you switch the tester on to show that current is flowing, even though the coil is not able to create sufficient voltage to arc across the air gap. So really you could hook up anything there, an analog voltmeter, whatever. I think most folks are wanting to recreate the original look.

[katy]

Originally Posted by shew01

The one I bought on eBay is missing the little neon(?) tube between the electrodes. Does anyone know what that thing is called or where I might find a replacement?

Electronics supply house, maybe an NE-51

Methinks I have some, PM me and I'll send you one.

[alexiskai]

Originally Posted by katy

Electronics supply house, maybe an NE-51

A self-contained bulb like the NE-51 won't help much, you would need a bulb with wire leads. The neon tube sits between two opposing springs, as seen in the attached image.

[Bob C]

Originally Posted by katy

Electronics supply house, maybe an NE-51

Methinks I have some, PM me and I'll send you one.

I looked up that number and most seem to show 120 Volts, how well will
they work on a few thousand volts?

[katy]

I have some like this, I could send, it's worth a try. Just protect your eyes in case the bulb "pops". Might need a resistor in series.

[katy]

Here's a picture of an NE51, with wires soldered on, connected across the output of a Model T coil. If using one I would put something like a 47K Ω resistor in series with it. The output of the coil was measured at just over 20,000 volts.