This article was first published in the January 1993 edition of Electronics Today International.
WARNING: there is a problem with the circuit ;-) C6 should be removed, or there should be a resistor in series with it ... I forget the exact number of ohms required, but it's a standard design
Page 1 (pdf)
Page 2 (pdf)
Page 3 (pdf)
Additional Contributions -- Mick Lacey (pdf)
OCR'ed version (doc)