Gents C7 electric master clock

[Robert Atkinson 2Participant @robertatkinson2]

I’m a bit of a “time-nut” in the electronic equipment sense. I have a few GPS disciplined clocks / frequency standards. And some atomic (Rubidium) references. I can measure time intervals down to a few 10’s of picoseconds.
I’ve always fancied a electromechanical Master Clock system. When a member of an electronics forum offered a Gents master clock and two slaves free for collection I was interested. Unfortunately collection was a 3 hour drive away. However, it was only a short distance from a family member who was coming to visit me about a week later. So I asked if they would pick up a couple clocks for me. They said yes. Seems I forgot to tell them one was five foot long! In my defence I hadn’t actually asked what the clocks were. Turns out to be a later mode C7 with integral slave and a couple mid-sized slaves.
First issue was while the pendulum had been removed to prevent damage, the case was locked and there was no key. Someone had slightly damaged the wood trying to force it. Thus a bit of locksmithing was in order. Lock appeared to be a high quality cabinet lock with claw keeper and pipe (tubular shaft) key. Having made a few measurements of the slot I visited the local Timpsons to buy a blank. They actually gave me a blank free of charge and said come back and pay for it if you can make it work. The bit on the blank was much too large So reduced that on the mill so it would go in and turn. Then blued it up, turned in the lock and then hand filed according to the witness marks. One more blue and file and it unlocked. Not pretty but it works.

[Michael GilliganParticipant @michaelgilligan61133]

A great start, Robert !

MichaelG.

[John HaineParticipant @johnhaine32865]

Have fun with it, and enjoy the clicking!

[peak4Participant @peak4]

A few links related to similar stuff which you may already know about
Light Straw, note the navigation menu top right after entering, which leads to lots of documentation
https://www.lightstraw.uk/gpo/clocksystems/

Some stuff on GPO Clocks
https://britishtelephones.com/menucloc.htm

And there’s an io group.
https://groups.io/g/electric-clocks/topic/a_strange_gent_s_gpo_type_36/95815827

I have a couple of ex GPO pendulum masters, but without integrated clocks, though I’ve not got either set up yet since we moved house.

Bill

[Robert Atkinson 2Participant @robertatkinson2]

Already joined the I.O. group. Further investigation of the parts shows the pendulum suspension spring is broken. Fortunately all the bits are there and the dimensions of the spring strip are available. I now need to get a bit of 15 thou thick, or more likely 0.4mm spring steel. As usual I’ll likely have to buy far more material than I need.

Robert.

[peak4Participant @peak4]

I’m not sure that we had any/many C7 models, but there’s a manual here, second post down.
https://mb.nawcc.org/threads/gents-c7-master-clock-docs-and-info.199686/

Bill

[John HaineParticipant @johnhaine32865]

Another useful information mine is clockdoc.org.

[Robert Atkinson 2Participant @robertatkinson2]

Yes, there seems to be plenty of information on the clocks.
One material that is sometime suggested for use as suspension springs is feeler gauges. However a set costs more than a big bit of stock. Additionally I would not particularly trust the material quality of some modern gauges.
While looking for suitable material I came across a seller on ebay with new old stock Peter stubs feeler gauge shim stock. They had the right thickness and width and 300mm length. Cost was a bargain £4.99 including postage in a plastic tube. So a length has been ordered.

Robert.

[duncan webster 1Participant @duncanwebster1]

A useful source of suspension shim is car feeler gauges.

I was offered a C7 by a friend, but had to turn it down, 2 reasons

• SWMBO decreed it was ugly, and
• even I would get fed up of the resounding KERLUNK every 30 seconds. You have to screw the clock to a wall, and the whole wall ten transmits the noise

I’ll probably clast some icons by saying this, but they seem much better engineered than Synchronomes, the suspension is a lot more rigid. I was given this slave mechanism some time ago, probably will never use it, so if you want it it’s yours for the cost of postage.

[John HaineParticipant @johnhaine32865]

I use 0.1mm beryllium copper shim for suspension springs – I have enough of the stuff for the worldwide horological construction community supplied as a free sample a few years ago, happy to send small amounts.

As Duncan says, the Gents like the ‘Nome is horribly noisy.  Many were used in strowger telephone exchanges where no one would notice anyway, or in factories schools etc tucked away out of earshot except for the slaves.  I remember the aeons it took on Friday afternoons for the minute hand of our school classroom clock to finally *click* round to 4 pm so we could go home..

On my ‘Nome I use stepper motors to drive both the gravity arm and the dial, almost silent, same could be applied to the Gents if you’re not insistent on originality at all costs. One stepper drives the minute arbor direct. A second has a spiral cam to lift the gravity arm.

[duncan webster 1Participant @duncanwebster1]

I think the clocks in telephone exchanges were PO type 36, made  by all sorts of firms to a common design. They were Hyp type, pendulum driven by electromagnet, not gravity arm. Much quieter,  but still decreed ugly by SWMBO

https://www.britishtelephones.com/clocks/clock36.htm

[John HaineParticipant @johnhaine32865]

Hmm.  Some sources say that the C-types were used in exchanges at least to some extent but nothing definitive. The Light Straw site doesn’t mention them.  Mostly Hipp toggle types then.

[Author]

Posts