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Sherlock Ohms

The Instance of the Recalcitrant Religious Instrument

October 19, 2009

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.”

Posted by Sherlock Ohms on October 19, 2009 | Comments (15)

November 15, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Glen Chenier commented:

Interesting story. KCH, in response to your 23Oct question #1, do a Google search on "Hammond Vibrato".

Briefly, a rotating capacitive scanner coupled to the tone wheel shaft picks off succesive taps of an electronic delay line. This causes phase modulation of the signal which we perceive as frequency modulation. (The explanations you will find through Google are much better).

November 9, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Uncle Ralph commented:

Interesting. Almost all Hammond woes in a foreign land are due to 50Hz vs. 60Hz power lines or comparatively low voltage. I've been worshiping Hammond Organs for close to forty years and this is one I hadn't heard.

October 28, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Vincent Pinto commented:

Indeed He has! And was, much more so while He was giving you all the wherewithalls up until that time to fix it.

October 23, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
KCH commented:

I have to set the record straight for Dick Wendt: I'm an old heathen so by all that's good & holy the Strobotac shouldn't have been there for me. But perhaps the Deity had in mind the greater good.

October 23, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
KCH commented:

From the author, a few responses (2nd time; 1st got disappeared.):
1. How was the sync-motor's speed to be varied for vibrato? That motor's speed is sync'd with the power line freq.
2. I myself own one of those oldies-but-goodies, a Model CAG 60175 made by GR for the Navy's BuShips. Not, I hasten to add, by having swiped the very one, but rather it's one I picked up from surplus decades later.
3. I'm currently working on a resuscitation of my 1-&-only Tesla coil. Stay tuned, as we coilers are wont to say...
4. I have to admit I never thought to check anything else in that organ. Sloppy...but long ago lost to history.
5. WildDave, I did find the "pitchfork", didn't I? And I bent it and am still here to tell about it.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Dick Wendt commented:

Here we have a case of the unusual: luck-on-the-side-of-the-righteous. If I had been there, there'd be no Strobotak available.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Steve commented:

The Hammond organs were an interesting and very mechanical design. There were no active electronics involved in anything more than the amplifier or the generation of the required synchronous "run" motor signals - the "start" motor described in Ken's article was momentarilly connected to 110v 60 hz - just long enough to get up the entire mechanism up to speed.
There were several mechanical quirks that could overcome the rather limited torque of the synchronous run motor and the symptoms Ken identifies were common. Why use a synchronous motor at all ? The answer was simple - by slightly varying the speed of the synchronous run motor, the pitch of the tone generators could be modulated very slightly - thereby producing a "VIBRATO" effect.
Despite their mechanical nature, many of these beasts operate to this day and are highly prized by a few for their unique sound and "attack" - despite some considerably lighter and much more compact alternatives.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Joel Goldberg commented:

There are still zillions of big, tube operated,
GR Strobotacs out there, and the users love them. They have a short, bright flash that has no peer, even after 50+ years. We own the product, and still make, service and calibrate these units They have 3 vacuum tubes (including the flash tube). See www.ietlabs.com.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
yonnie commented:

Holy cow! and I thought I'd been working in this field for awhile! Way to go Ken!! Maybe sparks from your Tesla has contributed to your longevity? Looking forward to reading more of your stories.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
DCR commented:

I used to work part time for an Organ Sales and Repair company in Des Moines, IA and worked on quite a number of those Hammond organs. In fact, I owned one for several years.
The problems we usually found were bad tubes or improper lubrication. They had instructions to oil them once a year with two drops of oil in each of the cups. The cups had wicking strings to direct the oil to the bearings. Each organ came with an oil can.
The organ I owned sat in a garage for several years before I took ownership. It had a similar starting problem, but all I had to do was lubricate it, since the bearings were dry.
Some people over-lubricated them, and that caused other problems. Sometimes the strings would break and the oil wouldn't get to the bearings. More often than not, they simply failed to oil it, and the bearings would dry out and it would fail to start. We 'repaired' many a Hammond organ with an oil can.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
unclejed613 commented:

they eventually replaced those tone wheels with optical disks and opto sensors, which reduced the inertia enough that the "starter" motor was no longer necessary.
i worked repairing banking equipment for a while, and built a blue LED strobe for an alignment procedure where the speed of a wheel was determined by the value of a fixed resistor. i then "calibrated" the strobe dial with the resistor values needed to correct the wheel speed. all a field tech had to do was put a mark on the wheel,"stop" the motion with the strobe, and install the resistor value shown on the strobe dial. the circuit board was not in a location where a potentiometer would have been a good idea.

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Ray Brohinsky commented:

Hammond organs are interesting beasts. We had one in our church for a while, and it also showed the exact same symptoms, but the fix was quite different: the tone-wheel mechanism is bathed in a low-viscosity oil, and the oil evaporates with time. Since no one knew anything about Hammond organs (before this), no one knew to refill the oil (nor what kind to use.) A Gulbransen repairman was actually the one who serviced the organ (apparently, at that time Gulbransen had some organs using the same technology licensed from Hammond) and taught me the ins-and-outs of tonewheel maintenance. The knowledge has long outlived the organ, sadly!

October 22, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
WildDave commented:

In retrospect, since the Devil was obviously involved with this breakdown, the first thing you should have looked at was something resembling a pitchfork.

October 21, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Simpler times commented:

I put myself through school servicing various electronic musical instruments. I "learned" the Hammond line from trial and error before I ever got my hands on a proper service document of any kind and I still have my hand-made wiring diagrams.
There were several mechanical problems inherent in the design that could easily overcome the sustainable torque of the synchronous "run" motor. The symptoms the author describes were very common.
The tone generator assembly wasn't the only electro-mechanical aspect of the Hammond design which was a maze of hundreds of rather fine switches all of which were actuated by the instruments' keys or the voicing slides. Other than the "Start" and "run" motors - the actual sounds were not produced or altered through other than completely mechanical means. Only the amplifier and "run" motor circuitry was of an electronic nature.
Despite a reliance on a a load of mechanicals - the line actually requires little in the way of maintenance and many of these instruments continue to operate today.
While modern electronics and "sampling" has encroached on a very close approximation of "the Hammond sound" - - Working B3's and other variants are still highly prized by performers who continue to value their distinctive voices and the "attack" of their keyboards.

October 21, 2009

In response to: The Instance of the Recalcitrant Religious Instrument
Bob Colwell commented:

way to go, Ken. Without that strobe display it's not clear how anyone would ever debug that situation, short of replacing one or both of the motors and accidentally fixing the tines along the way.

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