Electronic rev counter...

[Colin Morgan]

Another way...

http://www.da7c.co.uk/technical_torque_a...c_rev.html

[Stuart Giles]

Another way...

http://www.da7c.co.uk/technical_torque_a...c_rev.html

Blimey, Germanium PNP transistors in that diagram. Might be a challenge to find those nowadays.

[Colin Morgan]

It is amazing what is still around and how easy it is to find.  These are from 1982:

https://shop.pedalparts.co.uk/AC188K_PNP...25048.aspx

[richard wyatt]

I had great difficulty getting an electronic tacho to behave it jumped all over the place despite a return to the makers and allegedly their "latest upgrade".The A7 engine is electrically very "dirty".I solved the problem very simply with a suppressor of the TV sort costing a few pence in the HT line.

[Steve Jones]

I use a 12 volt electronic Rev Counter in my Ulster, Ruairidh. Supplied by Willie McKenzie and not cheap but it looks the part which is important. I also have a cheap, modern, Durite electronic Rev Counter in my Trials car where looks aren't quite so important!! Both simply take a signal from the coil. Neither have the problem Richard reports above. However, if the cars are left in a damp atmosphere, say overnight at an event, and they pick up a bit of damp air (evidenced by moisture on the glass internally) it can play havoc with the car's ignition a problem simply solved in the interim by removing the plug from the rear of the unit. Only happened to me once at a very wet Prescott some years ago but it caused some head scratching until a friend told me how to solve it based on it happening to him.

Steve

[Alan]

Mine has a simple toggle switch which switches off the tachometer for when this problem occurs. It does very rarely, however the other use is you can switch it off if you are looking for a fast run and don’t want to be bothered by technicalities.

[Michael D]

I've got this 12 volt OS tachometer in the Rosengart (with a 12 to 6 volt converter...) https://boutique.techni-tacot.com/moteur...voire.html it's negative earth.. not the cheapest solution but at least it looks 'a bit' classic.

[Ray White]

Something that is perhaps not that well known is that if one or more relays are fitted they can send out a voltage spike that can seriously mess up any electronics.  The relay should be replaced with one that has a built in diode.  A similar problem can occur with electric petrol pumps; in that case a transil or varistor should be wired across the points.  Probably not relevant in this case.

[Roland Alcock]

I was curious about what speed my engine ran at (3 bearing standard spec) and spent a tenner on a nasty plastic inductive one. It has its own battery for powering it.
https://m.media-amazon.com/images/I/61WC...SX679_.jpg
My conclusion was a max of 3000 rpm was comfortable.
Roly

["Slack Alice" Simon]

I use one of those self contained little gizmos.Very unobtrusivr, easily fitted and removed, works very well.

It is double sided taped on a thin ali bracket, folded to hang off the lip of the glove pocket.

Bracket painted black, all you can really see are the numbers.