David Chapman via EV wrote:
Jan, thanks for the input on this. Lee I really appreciate the lead
on the GE handbook, I downloaded it and indeed that circuit on pg 293
looks perfect for this project...

One question tho, you said something about it needing a capacitor and looking 
at the
schematic I don't see one...

Fig 10.5 is a "quick-n-dirty" circuit that works, but has issues at the low-speed end. Have you used a cheap light dimmer, and noticed that the brightness is unstable at the dim end of the range? Same thing with that circuit; the motor speed will be unstable at the low end.

Look a little farther in the book, at fig. 10.6 and 10.7. These are improved circuits that add a 0.2uF capacitor and 2N4987 trigger device.

The 2N4987 is an oddball part from GE that is hard to get today. Newark has them for $5.68


The 2N4987 is what GE called an SUS. It is really just two transistors (one NPN, one PNP, a resistor, and a zener diode). These are all 10 cent parts, so you can make it yourself. The GE datasheet shows the circuit.

Or, you can replace it with a modern part. Every manufacturer has a different name for it. Common variations are SIDAC or DIAC. I'd try the MCC DB3-TP, www.digikey.com DB3-TPMSCT-ND $0.21 each.

Thanks again, I really appreciate you you taking the time to offer
advice. Dach.

You're welcome! Best success with your project. :-)
It is vanity to do with more that which can be done with less.
        -- William of Ockham
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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