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SWCC SWCC master / slave difference


New Member
Jul 6, 2020
Ok first I’m a newbie and A novice
I found this form while researching my newly purchased self winding clock company model F movement
About a month ago I purchased a self winding clock company movement on eBay
it did not have the case, but everything else seem to be there
my father used to make Clock cases for a hobby. I wanted to take a crack at making my first case. I got the Clock case made and I wanted to make the whole Clock a skeleton type display, so you can see all the parts.
Earlier this month when my birthday came up my wife asked me what I wanted and I thought “sure would be nice to have a master slave set of clocks“ So I bought another self winding clock. again on eBay and this one Has the square metal case and it has the light fixture for the signal
my questions here are
What’s the difference between the master and the slave clock? Isn’t the master clock really a slave to the signal that it received. I believe the master clock received a signal once a day, and as I understand it save clocks received a signal from the master clock once an hour.
I have bought the kit from kens clock Company But I would like The bigger clock that I made the case for to actually send a signal to a smaller clock that I got for my birthday so when the kit from Ken’s clock company sends a signal to my larger clock can’t it also send a signal to the slave clock.
Is there a real Physical mechanical difference between Slave and master clocks also I believe the lightbulb that was in my smaller clock is of the wrong type & wrong voltage I believe it’s a 14 V bulb
the 3 volts barely light it up
I was wondering where and if I can still get a three volt bulb for this.
The bulb socket is currently a bayonet Type

Tim Orr

National Membership Chair
NAWCC Fellow
NAWCC Member
Sep 27, 2008
Boulder CO
Good evening, Dor!

If you have been in touch with Ken's Clock Clinic, I would certainly suggest referring some of your questions to Ken. I know no one more knowledgable than he. I have never actually seen an SWCC "master" clock. Since these things were synced by Western Union, it would have been pretty much as easy to sync all the clocks in a system to the incoming signal from WU as to sync subsidiary clocks to a house "master." In any case, the "master" really isn't a master, being a slave to the Naval Observatory.

If both of the clocks you have are slaves – which I'm betting they are – you can simply parallel or series-wire (ask Ken) from his synchronizer, and sync up both clocks at the same time.

All later SWCC clocks synced once each hour, at the top of the hour. It would be a bit tricky to synchronize the master once each day, then the slaves once each hour. For a new light bulb, that admittedly can be tricky. Again, though, I'd bet Ken would know a source.

Good luck and best regards!

Tim Orr


Registered User
Oct 27, 2011
Master SWCC clocks are uncommon. Most of the smaller clocks were synchronized to Naval Observatory time by Western Union. And the larger clocks tended to be used for high accuracy stand alone applications, a jeweler's shop for instance. A master isn't usually sync'd to another time source, because it is a highly accurate timekeeper itself. SWCC made several grades of movement, the best had gravity escapements. Typically, you would see at least a 60 beat clock used as a master. When used as a master, the clock would could have one or more pilot clocks, each of which would operate with a string of slaves. This allowed a single master to operate dozens of slaves. Some systems evem allowed the slaves to be set through the pilots. You'll find lots of long case ITR and Standard clocks set up as masters, because these were frequently used to operate school and factory systems. What you're looking for is something like this:



Registered User
Jan 28, 2010
Bethlehem, Rural NW CT
Here are some pictures of a SWCC master style movement that is equipped with contacts that operate once a minute and twice a day (8:30 AM and 8:30 PM), there also is no synchronizer and no mounting holes for one. I have seen one other like it, mounted in the typical square metal case like the Western Union clocks.

DSC_3292.jpg DSC_3293.jpg


Registered User
Dec 11, 2009
Houston, Texas
The syncing came every day at noon. Mine had the later “chatterwind” movement. Above and to the right was another set of coils. Every day at noon, a signal was sent to the secondary movement. It energized the coils. The coils would pull down a “saddle” over the minute arbor on the clock. If the clock is within five minutes of noon, the saddle would correct it to straight up noon. Mine had a bell. When the signal came, it also rang the bell.