Anyone understand the start stop on a Columbia Gothic?

[melvind]

The reason for making this video was to show how the recently repaired start and stop mechanism connected under the motor board to the tone arm of this beautiful Columbia Gothic Grafonola. It is a very complicated gear based “thing” somewhere between a differential and a transmission (perhaps not the best description). There are some pictures below.

A friend helped me get this working again. When I purchased the machine the tone arm was locked up and the start and stop would not function properly. I had removed the gear housing so I could play records on the machine manually. But, the motor never did play up to speed and I have always wanted to get it back together again. Thanks to my very helpful friend it is now all back to functioning perfectly. Neither of us knows exactly how. He is also on the forum so perhaps he will chime in with additional information or corrections to this post.

I must admit I don’t fully understand how the mechanism knows when to shut the turntable off. No matter what size record or how large the runout on the record is, the turntable stops after about 25 revolutions at the end of the record. I am guessing it must be able to detect the lack of movement or something along those lines. The gearing visually seems to hint at some type of timing is involved. Perhaps someone will know more how this actually works and give me some additional information.

The record is “Good Bye France” by Nora Bayes from 1919. A cute little World War I song sung by a very famous Broadway and popular singer of the time.

[youtubehd]http://www.youtube.com/watch?v=DKVTrsy-tGU[/youtubehd]
https://youtu.be/DKVTrsy-tGU

[OrthoSean]

That's a real looker of a machine, Dan! Got me on the start / stop mech. I always thought when the tonearm stopped moving forward, it tripped the mechanism. It's a simple looking mechanism that always seemed to be tricky when I tried (and failed) to repair one.

Sean

[alang]

That is a gorgeous machine! I hope you will present it as a Featured Phonograph some time.

Andreas

[melvind]

That is a gorgeous machine! I hope you will present it as a Featured Phonograph some time.

Andreas

Andreas,

When I get some time later this week I will put a Featured Phonograph post up. I need better pictures and some time to write things.

[coyote]

Perhaps the patent for the auto stop would shed some light on it, if a number or some starting point could be found to research it! Interesting mechanism in a lovely machine.

[startgroove]

Always fascinated by unusual mechanical devices, I was very interested in taking on this project for Dan. I'll attempt to describe the operation of this automatic shut-off device here. (Please forgive the technical description.) The pot metal swelling had locked the tone-arm beyond use. In addition, the motor would not come up to speed. The latter was easiest to fix and was the first task I undertook. The second part was far more arduous.

My initial tests showed that the transmission like box appeared to be sticky and erratic in operation. This box had two inputs, one from a rotating shaft which came off the motor and was precisely geared to the rotation of the motor, and the second was from the tone-arm and was actuated by a gear at the base of the tone-arm. Upon removing the cover, I recognized a differentiating set of gears. They seemed to compare the rotation of the motor to the position of the tone-arm. The output of this mechanical comparator was linked to lock on a switch, and the lock would released when the input from the motor exceeded the input from the tone-arm. (That switch was closed and locked as the tone-arm was swung to the left.)

Put more simply, the position of the input from the motor is compared to the position of the tone-arm. When the tone-arm stops advancing (at the end of the record), the motor input continues to move until it triggers the switch to release.

This arrangement eliminates the need for a spiraling lead out groove on the record, so it will work with early acoustic recordings. Nor does not care what length the recording is, or where the ending groove is. In addition, if there is ever a case where the tone-arm does not advance, such as with a repeating groove, it will shut down the turntable. I suppose you could add that it does not infringe on the patents of others.

I want to thank Dan for allowing me the opportunity to learn about this device, and this amazing machine. To me, it is a marvelous engineering accomplishment. I am in awe of the capabilities of the Columbia designers who created this device.

Cheers, Russie

[melvind]

Russie, thanks for the wonderful description of the device that turns the motor off on my machine. I know what it does and I understand your description but I am still having a bit of trouble grasping exactly how it accomplishes the shut-off (recognizing that the tone arm is no longer moving). But, I am so happy to have the machine working perfectly once again. I am so grateful for the help and fantastic technical skills involved in this fix. We have a great community of phonograph folks!

[Phototone]

Would this be the same mechanism that is found on the spring motor Columbia machines of the same period?

[melvind]

Would this be the same mechanism that is found on the spring motor Columbia machines of the same period?

I don't really know, but since the shut-off device here is an electric switch, I have doubts they use same technology for windups.

[startgroove]

Phototone: None of my spring motor Columbia's have this kind of set-up. A couple of my electric motor powered Columbia's from this period have the same white porcelain switch to apply and disconnect power to the motor, but none have the mechanical comparator. On those, the tone-arm must be returned manually to outside the edge of the record, for shut-off. Cheers, Russie