Aftermarket tachs: how do they get their signal?

[mr-asa]

Got in a conversation over PM with Bill over his twin Javelins and tachs. We started to wonder if there was a transmitter box or something on the motor side that told the tach what to do.

I saw something that indicated there might be one, but I’ve never seen one on eBay so maybe they are getting left on motors. However Bill said that in his collection of OMC motors he has never seen one.

Anyone have an answer for us? How do aftermarket tachs get their signal? In particular Bill and I were talking about the Airguide tachs.

[frankr]

Some used a transmitter, matched to the motor, such as Airguide and Aqua Meter.. They were generally mounted behind the dashboard and got junked with the boat. OMC Accessories’ Universal Tachometer did not need one.

[bill-mcnamara]

Frank, I would love to learn more about the "Universal Tachs". Any leads appreciated.
Bill.

[frankr]

OK, so I called it by the wrong name. Should be "Standard Tachometers" This page from the 1974 OMC Accessories Catalog.

[jeff-register]

Frank,
We had a 56 Buick we did 4 wraps on the plug wire & get enough signal to turn on a scr or a Q, early for darlington design. It fired neon lights under the dash. Think they all used a buffer & a solid state conditioner to feed the tack with a signal. Not bad just energy gobblers,

[58fourfifty]

This is a typical Airguide set-up with the transmitter.

Verne

[mr-asa]

I think that’s the first I’ve actually seen, Verne.

Is that yours?

[58fourfifty]

Yes, that’s mine, but I don’t think I’ll use it since it’s a 7K rpm tach and the motor is rated for 5K max. I’ll be using one of these: a 652B and 653B. They all take senders.

This is the 653B sender

I think a tach is a great asset for setting up your boat properly. If the motor is rated for max power at 4500rpm. then you can prop it to achieve 4500rpm at full throttle. The ones shown are all NOS. I have another one (not shown) that is a flush mount, which means drilling a large hole in the dash. I’m not sure I want to do that. I like the fact that the Airguides have that large "football" on the face to match vintage OMC gauges.
Verne

I don’t know if it’s ok for me to post this link or not but you can find out a lot more about them here:
http://forums.iboats.com/Marine-Electronics/Airguide

[mr-asa]

Does it come apart at all? I’m assuming that the inside is filled with some insulating silicone rubber like RTV.

If it can be opened up at all I’d appreciate some high-res pics of whatever you have in there (if anything’s visible)

[58fourfifty]

I don’t believe it’s meant to be taken apart and I wouldn’t risk trying on mine. I doubt that it’s filled with any kind of sealant though. The instructions say to mount the sender at least 15" away from any magnetic source, such as a compass.

Verne

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