Tinker Dwight suggests that the earphones I used were high-impedance magnetic.
Yes, they were electromagnetic, not piezo-electric. They were simply branded "American Airlines" and have a significant DC resistance of about 60 ohms.
This, I believe to be a significant series impedance which put the KundO's transistor-solenoid circuit into audio frequency oscillation at each stroke of the pendulum magnet resulting in an oscillating audible sound in the earphones which was interrupted at the critical points in the pendulum magnet motion.
In retrospect, I should have repeated the experiment using a non-functional KundO battery clock.
I'm thinking it would be a good idea to continue this electronics discussion off-line using PM as we are straying away from horological discussion.
Some excellent reference stuff has been brought to the foreground. We owe big thanks to dietrich and to Uhralt for the excellent and useful KundO reference material and drawings. Kudos guys.
