I posted a schematic and theory of operation of an improved version of my
attempt at this. It triggers nicely to about 1MHz with the parts as shown.

http://www.novatech-instr.com/Fun/trig.pdf

Thanks for all the feedback.

Steve.
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Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA