Inductive pickup for a tachometer

I found some very usefull information in an earlier post about this subject, and bought the pickup sensor shown in the attachment on eBay. I compared the electronic diagram of this clamp (see 2nd attachment) to the actual clamp and I noticed a few differences: The diode closest to the coil is a 1N4007 and not a a 1N4148 (not a big deal I guess), but the resistor in the clamp has a value of 10M, and not 1k as shown in the diagram. Should I modify the 3k3 resistor to another (higher?) value?



If it works use it, not all designs are the same. The 1N4148 is a fast diode but does not handle a lot of current. By changing the 1K to a larger value transfers more energy to the SCR gate. Not all SCRs are the same and trigger with different amounts of gate current and voltage. It may not be even made by the company that made the one you are referencing.

There are more than a few ways such a circuit can be designed. You should at least give the Manufacturer the
benefit of the doubt. It is unlikely they released it for production without extensive testing. Have some faith.

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