Many thanks for that. I incredibly don’t have a variable bench power supply but know someone who does. Job for next week I think.
I finally found the site I used when I first fitted the clock. It’s very helpful:
http://www.rogerj.co.uk/PO%2036.htm
I’ve also attached a photo of the current wiring. Looks like the dial slave is running directly off the pendulum supply.
I hope to initially run one slave. If permitted might run the other 2 into the house but that’s still under negotiation!
Thanks again for advice.