Now is the time...

[Donald]

Won an eBay auction for a classic white faced IBM wall clock. Has standard AC plug. The works have a circuit attached consisting of a vacuum tube, a few caps, 2 coils and a solenoid. The model is a 56-45. From what I can find it has the capability to correct itself after a power failure for up to 12 hours.

When plugged in the sweep second hand runs up to 12 then stops. Then the minute hand starts advancing at an accelerated rate with the hour hand following at the corresponding rate. After advancing a few hours the sweep hand starts and the clock starts running normally.

Now the problem. There is no way to set the clock. I am beginning to think this clock needs some external method to set it and then it runs on its own.

It appears it was made before Zip codes. The label on the back says New York, 22, NY

Ideas?

[Zilch]

Think back to your days in school. All of the clocks were slaves to a master which set them to keep them synchronized....

[Donald]

This is true. Whatever sent the sync pulses did it over AC wires. I guess I need to find that unit.

And it would be nice if the eBay sellers of these clocks mentioned that. :)

[Art J.]

I remember installing these systems in schools
when I was a young Electrician. Here is a link
that will be useful.

http://www.setclocks.com/index.htm

[speakerdave]

When plugged in the sweep second hand runs up to 12 then stops. Then the minute hand starts advancing at an accelerated rate with the hour hand following at the corresponding rate.

Do do remember how much we enjoyed this when it happened at school.

David

[sonofagun]

I always liked Mr. Spock's solution to everything...


"Cross-circuit to 'B' "

:D

[Donald]

I got some info from a guy that runs a website for Standard clocks.

Every hour between xx:57:52 and xx:58:02, an impulse is sent out, in this case, at a certain frequency imprinted on the AC current which the vacuum tube arrangement picks up, and activates a magnet in the slave movement. This causes the slave clock to go into correction mode... basically it says "if your minute hand doesn't read :59 by :59, then make it happen."

At 5:59:02 a.m. and p.m., and additional impulse is sent out (until 5:59:08 I believe), which basically tells the slave clocks, "If your hands don't read 6:00 p.m., get there", in which the clocks corrects itself to 6:00. If it's way off, it'll get there but a few minutes late, and then catch up at the 6:57:52 using the first method.


Now all I have to do is find info on the transmitter. :)

[sonofagun]

That's what Mr. Spock means by "Cross-circuit to 'B' "

:beamup:

[Donald]

Just got some more info.


Don, the frequency you will need is likely 3510cps. The back cover of the movement should confirm this. The only difference between the 6:00 correction and the other corrections is that the other corrections are 8 seconds and 6:00 is 14 seconds. If you live in a large metropolitan area and are close to one of these systems, you might be able to pick up this signal in your house. Most of these systems were not too well filtered. Harold


Anyone willing to design a circuit to inject a 3510Hz sine wave 10v P-P onto the AC line?

If it comes, I will build it. :)

[hector.murray]

might not be too hard. A crystal oscillator on a 12 or 15vdc supply with an emitter follower maybe. Need a 3.5KHz crystal.

[Donald]

One thing I am not sure is how to protect the unit from the 120VAC it has to be connected to.

[hector.murray]

Well, a simple 60Hz filter with a 10meg path to ground should work. or, easier yet would be to find the 3.5KHz input path and apply the signal direct there. Since this is just the one clock, you need not ride the sync signal over the AC line as you would in a school, where the master clock would need to feed multiple clocks. I'm curious though. Would you need to feed the sync signal to the clock continously, or just at the selected times?

[Donald]

As I understand it, just at the selected times.