Gents C7 - adding a C69 Bell controller

Richard Kemp

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Nov 11, 2017
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Hi all,
I am new to this forum and was hoping for some advice. I recently purchased a Gents of Leicester C7 Master clock (#5933; circa late 1950s I think) which after a little adjustment is now running very nicely from a small 12v sealed led acid battery with a solar trickle charger attached. I would now like to add a C69 bell controller which I have also purchased (slightly more recent vintage from a school in Northern England). My question is how to add the C69 to the circuit. I have tested the C69 and it works well. I know it needs to be in series but as I can't trace all the wiring in the C7 I am a but nervous about attaching it. The C7 has two large terminals one on either side of the case. I have used these to connect the power and all works as it should. But where should the C69 be wired. I am concerned that I may need to change the wiring to the internal slave built into the C7 to ensure everything is in series. But surely Gents would have made it easier that this??
Any advice would be appreciated.
Richard
 

Edwardo

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Jun 18, 2006
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Hi and welcome

There were a few different ways to wire these clocks
If you post some photos of the wiring it would help confirm the correct way to wire your version

However the most common way is as follows;
The slaves are connected in series (daisy chain)
So simply remove one of your power connections from the c7 and connect it to the c69
Connect the other terminal of the c69 back to the power terminal on the c7
If you are using 12vdc you will need to adjust the large potentiometer in the c7 so the current on the circuit
is approx 250ma


Hope this helps
Edd
 

Richard Kemp

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Nov 11, 2017
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Many thanks.
Here are some photos of the C7 and the C69. (The mercury switch has been removed form the C69 for transit).
The critical one is probably the third photo. The grey wire connected to the terminals on the two sides of the case attaches to the 12V supply.
Regards,
Richard


IMG_0425[1].JPG IMG_0431[1].JPG


IMG_0427[2].JPG IMG_0429[1].JPG IMG_0432[1].JPG IMG_0433[1].JPG
 

Edwardo

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Jun 18, 2006
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Hi Richard
Your clock is early 1947 (possibly February )

On the attached diagram RED is positive

Remove the positive battery connection from the clock and wire it to the + of the c69
connect the - of the c69 to the + of the clock
Adjust the resistor to give you 220ma to 250ma at the contacts (see photo)

If you need more info feel free to PM me
Cheers
Edd
C7 wiring.jpg
C7 wiring.jpg
 

Richard Kemp

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Nov 11, 2017
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Many thanks Edd. I have done all that and the C69 is now working. I find it difficult to measure the current so have slowly reduced the resistance until there is just enough current flowing to reset the gravity lever. How do you manage to measure the current accurately? I have seen a suggestion that you can hold the contacts closed - is that safe?

Thanks also for the confirmation of the date of the clock - its older than I realised.

Richard
 

Richard Kemp

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Nov 11, 2017
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I have just measured all the resistance values (variable resistor set to 23 + 4 for internal clock + 18 for C69 = a total of 45ohm). Given I have a 12 volt supply that suggests a current of 267mA - I guess that's close enough.
Richard
 

Edwardo

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Jun 18, 2006
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Place a piece of card between the c7 contacts and put one probe on each of them
The magnet will energize so watch you fingers

the pilot dial is 4 ohms but the main coils are 15 each (total 30) and the c69 you say is 18, the resistor 24
total 76 ohms @12vdc = approx. 158 ma

If you wound the resistor to zero you will have 52 ohms which should give you a working current of approx. 231ma
 

Richard Kemp

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Nov 11, 2017
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Ah yes, I forgot to allow for the coils in the C7. I have backed the variable resistor off a bit more and the C69 sounds a bit happier - it was a little sluggish before.
Thanks again for so much very helpful advice.
Richard
 

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