Divine Intervention or a clever engineer at work? You decide.
By Ken Herrick, Contributing Writer
Fifty years ago and more I was a Collins Radio Co. field engineer at a former Kamikaze base turned U.S. Navy base in Japan. One day the base Chaplain, rather improbably, called upon me. His Hammond organ was repeatedly failing to turn on; could I help? So I went to the chapel and took a look. Sure enough: almost every time I tried to start it, it would seem as if it was starting but then it would shut off.
The Hammond organ, at least in those days, was an electro-mechanical device. It incorporated a long shaft on which was mounted a string of shaped, magnetized disks. The shaft and disks rotated, driven by a synchronous motor. Adjacent to each disk was a coil, which picked up the varying magnetic field and whose output current was then summed with the others, via the keyboard’s key-switches, and amplified to produce the sound. A shaded-pole induction motor was also mounted on the shaft, whose purpose was to bring the synchronous motor up to near-synchronous speed at start–that motor being incapable of starting on its own.
The procedure was to momentarily press a start-button to energize the shaded-pole motor and bring it and the other elements up to the near-synchronous speed. Then, when the button was released, the induction motor would de-energize, and the synchronous motor would take over.
So while looking closely at it, all would appear normal almost every time, except that the shaft would shortly come to a stop. Scrutinizing it more carefully, I thought I could see a kind of hesitation at the coupling between the two motors and the disk-shaft.
It happened that the base’s shop had a General Radio Strobotac, a stroboscope and in those days, big and tube-operated. So I set that up to illuminate the coupling. Having adjusted the strobe rate, I then initiated starts and the source of the problem became apparent. For a reason I didn’t trouble to analyze, the motors were coupled to the rest of the shaft assembly via a pin-and-fork, which provided for a bit of rotational decoupling by virtue of the spacing between the pin and the “tines” of the fork.
At the moment when I released the pushbutton, I could see–in slow motion, so to speak, due to the synchronized illumination of the stroboscope–that the pin would bounce between the fork’s tines such that it would impart a slight shock to the motor shaft in the direction against rotation. That apparently was enough to knock the synchronous motor out of its phase-lock and bring the whole thing to a halt.
So what was the fix? Merely to bend very slightly a tine of the coupling-fork until synchronism became properly maintained. After that, no more problems–and surely God has looked more kindly upon me to this very day.
Contributing Writer Ken Herrick has always been in his words a techno-nerd. “I spent 18 months in the Navy, then a BSEE from U.C. Berkeley. Worked for “The Boeings” in Seattle but didn’t fancy the drudge-job–or the rain. Then as an airline station-agent in Alaska (not much rain but too cold). Then it was the Rad Lab in the Bay Area, designing stuff for the 1st A-bomb test at Eniwetok. Then I got married and we took off for our field-engineering sojourn in Japan. Then back to the U.S., but this time the long way, docking at NYC flat broke and with first-born bringing chicken pox. Took a 4 year job in RI as a project- and system-engineer, then back to CA for various engineering employments over the years. Along the way, my mother’s art-gene kicked in. Did kinetic and neon art for 25 or so years, then spent some years (retired) Tesla-coiling, and…here we presently are.”
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