John
I have been doing some work to reverse engineer the Smith's RVI tachometer. I have done a couple of rebuilds using new transistors, capacitors and thermistor and have achieved linear indication from 0 to 7000 RPM. The thermistor is not easily identified. Tom Haydon of the Sunbeam Club has done a lot of work to identify this device and we think the 330 ohm 3560k rating is close to the original. I am currently working on a temperature controlled box to see what low and high temperatures do to the calibration. Send me your email address and I will send you a .pdf of the attached .jpg drawing. This is a preliminary drawing as I work through design and bill of materials. I am planning a 3 part article for the Healey Marque magazine starting in January showing repair and calibration.
Bill Young, BJ8, BN2, AN5
sjahc.com