Michael
Forget the resistor and the idea of running the clock from “D” cells
“D” cells, because of their design will not last more then a few weeks
The problem you describe indicates there is enough voltage but not enough current (AMPS)
The batteries referred to in the manual were large lead acid batteries that could deliver many amps. (similar to car batteries).
“D” cells can’t give the sort of service the clock needs
If you run this type of clock off “D” cells you will find that within a week the batteries will start to fail and probably leak nasty stuff all over the place
For what you are trying to do you don’t need the resistor to start with.
All that it is doing is sucking more power (amps) out of the circuit
Think of amps as the power water travels through a garden hose
And the clock coils as empty beer cans on a wall
If you point the hose at the empty beer cans the water blows them away
This is because the water is coming out powerfully
If you reduce the flow through the hose pipe by standing on it,
the water pressure drops and there is not enough power to knock the cans off the wall
The resister you are using is working like your foot on the pipe
So what you need to do is turn up the pressure (amps) to get the coils to operate
The only way to increase the Amps is to use a heaver duty power supply
Your “D” cells can’t deliver this type of power, so after time they will self destruct
It is not possible to burn out the coils in your clock with the type of batteries you are using
Nor is it possible with a small 12v dc 3 amp power pack
The worst that will happen is the coils will start to warm up if they are energised for a long period of time (30 seconds or more)
You are more likely to destroy the batteries or supply first
Current Diagnostic
If the current is to low the master clock or slaves won’t work
If the master clock works, but slave does not, the current is still to low
If the master clock works and so does the slave, BUT the slave misses pulses or jumps on extra minutes the current is to high or very sightly to low
You really need to invest in a power supply that is at least 1000ma (1Amp) 12vDC output
Worry about the resistor later
Edd
NOTE
BTW
Tom is correct about the spark issue
It will eventually burn out the contacts (a few years)
The old fix for this used resistors and capacitors. This worked very well.
The new fix is some 2 cent rectifying diodes that can be bought from any electronic parts supplier (radio shack??)
Simply wire one across every coil, (only one on the master clock across the terminal block on the main movement)
Make sure that the stripe (on the diode) faces the (+) side of the circuit
There has been a lot posted on this forum regarding the rights and wrongs of spark suppression
I use diodes because they are cheap and they work
They are small enough to hide behind other clock parts and do not alter the clocks originality in any way that may devalue it.
In your case, Michael I wouldn’t worry about the diodes until you have the supply sorted
Nice clock Tom