The Pulsynetic C7 Master Clock


A view of the Gents' C7 master clock pilot (slave) dial with the case door closed.

Only the top of the clock case is shown. The master clock's two electro-mechanical movements are hidden by the dial. The main movement (painted green) keeps the pendulum swinging and the time circuit impulsed at very precise, half minute intervals. The slave movement simply advances the pilot dial in the case and is similar to all the other slave dial movements.

Some Gents' master clocks (C6) were sold without a pilot dial so that the movement could be clearly seen behind the door glass. A pilot dial is very handy if there are no slave dials in the immediate vicinity of the master clock to allow one to monitor the timekeeping. Fixing a slave dial to the wall near the master clock easily overcomes this problem and gives a choice of dial to match one's taste or d├ęcor. The advantage of having a pilot and at  least one other slave dial is that comparisons will quickly indicate whether a fault lies with the clock itself or a single dial. 

A view with the clock case door opened appears below. The brass mechanism on the right  is called a slave movement. It is usually hidden behind the steel dial plate and drives the hands on the pilot dial in 30 second steps via a 120 tooth ratchet wheel and a small electromagnet. The small gears visible (horological term for gears = wheels (large) or pinions (small)) are the motion work for driving the hour hand from the minute shaft. (horological term for axle = arbor) The pilot dial is placed in series with the master clock's own electrical contacts and all the other slave dials and half-minute impulse mechanisms in the time circuit.

 Inside the Gent's C7 Master clock case.

Gent's (pilot) slave dial.

The small gears visible through the large ratchet wheel is the motion work for driving the hour hand from the minute shaft. In a 12:1 ratio.

I have already mentioned that the master clock is entirely responsible for the accurate timekeeping of the WT turret clock movement. The master clock has a 1 second pendulum, driven at half minute intervals by a falling weight. The weight itself is a long, bronze-coloured, metal lever. This is pivoted at one end and has an attached roller at about the mid point. When the gravity arm is released by the catch (at the free end of the gravity arm) the roller runs down the impulse ramp on the pendulum and gives the pendulum a gentle push to keep it swinging. It sounds easy but the invention of a reliable roller and ramp mechanical impulse system only became possible with the aid of electricity to rapidly reset the gravity arm. The advantage of a half minute impulses was the relative freedom of the pendulum in between impulses.

The roller and ramp provide a gentle push with exact repeatability of the same action again and again. Always around the centre of the pendulum's arc where it can do least harm to the timekeeping. The vital factor is that the energy the roller puts into the ramp on the pendulum is almost unchanged from one half minute. And the next and the next for literally millions of gentle runs of the roller down the ramp. If the push is exactly the same then the arc (total swing) of the pendulum will not change and nor should the timekeeping. The mechanical roller impulsing system also found favour in competitor's master clocks.

The exact details of the shape of the ramp and the size of the roller have been modelled mathematically in the search for the best possible timekeeping. In between receiving these gentle impulses, the pendulum is free to swing. Except for the light duty of gathering the escape wheel. Most mechanical clocks are constantly interfering with the pendulum through the escapement. The master clock offers far less interference with the pendulum as a timekeeper. In fact some master clocks can compete for accuracy with regulators. A class of clock where absolute accuracy is their prime purpose.

Thermal compensation of the pendulum is also essential to good timekeeping. The flat pendulum rod of the Gent's master has diagonal lines scribed on the front. This to show at a glance that it is made of low expansion material and not simply a strip of bright, mild steel.

Everything in an electrical impulse clock system relies on the master clock's rate (timekeeping) to remain as stable and reliable as possible. The master clock case would usually be locked to avoid worker's cheating so they might come in late and go home early. Machine running times were often monitored by a recording device controlled by the master clock. Lost time meant lost money in industry. Many factory workers were paid for piece work. Meaning they were paid on their daily or weekly personal production total of the items being manufactured. This system ensured that all worked as hard as possible just to make more than a bare minimum wage. Machine "down time" was a disaster for both the management and the workers. Devices were invented which could monitor the actual run times of the machines in a factory. These relied on the half minute impulses from the master clock to ensure accuracy.

Factory sirens, whistles or bells controlled by master clocks via contact programmers were once commonplace. As were clocking-in machines at factory entrances with wages lost for late arrival. Being a few seconds late could cost a quarter of an hour's wages. Or even more if lateness occurred on several days in any week. Mass production required that all are present on time for the many, inter-related tasks to run smoothly and achieve maximum rates of production. Penalising the late riser in their pockets was one way of ensuring punctual arrival times. It was essential that all clocking-in machines showed and recorded the same time or there was "trouble at the mill". An impulse clock system ensured uniform time throughout the establishment.

Problems sometimes arose when there were regular queues at the clocking in machines. The timekeeping was accurate but the sheer weight of worker numbers in some factories defies description by today's standards in the West. Much work was very labour intensive and repetitive with many thousands of workers in any one factory building. Or spread across a whole complex of buildings. All joined by the thin wire which brought the impulse time system to every corner of production and office work.

Before the age of CAD (computer aided design) drawing offices were often vast areas. Sometimes housed on several floors. All closely packed with desks and drawing boards with aisles in between them. The number of slave dials supplied to a large factory was often beyond everyday imagination. Manufacturers of impulse time systems would list their most prestigious customer's installations in their advertising brochures and leaflets to emphasise their capacity for supplying literally thousands of dials on a single order for a complete timekeeping system.

Meanwhile, back at the vital master clock which controlled it all:

The impulse roller can be seen below (arrowed) resting on the ramp in this posed image of the master clock movement below: Normally the run of the roller down the impulse ramp and resetting is far too brief to be caught on a still camera:

The Gents' Pulsynetic master clock movement. (1961)

Above the impulse roller can be seen the 15 tooth gathering (or escape) wheel. This wheel is pushed round, tooth by tooth, by the gathering pallet as the pendulum swings to the right. At half minute intervals the gathering pin rises into a deeper notch between two of the teeth of the wheel. The gathering pallet extension rises and pushes the gravity arm catch aside so that the gravity arm can fall. The roller runs down the ramp, closes the electrical contacts and the gravity arm is then instantly reset on its catch by the electromagnets. The contacts can be seen at the bottom left of the movement and in the image below:

Close up of Pulsynetic Movement contacts.

The closing of the contacts and rapid reset of the gravity arm provides a short, highly accurate, impulse of DC electricity which can be used for a multitude of tasks. All that is required is a low voltage insulated wire to be taken to wherever a very accurately timed impulse is required. Often this is over quite large distances within a factory complex or hospital. Instruments, dials and other mechanisms are all placed in series with the master clock contacts and all of them will keep time as accurately as the master clock itself.

The image above shows the gathering pin resting in the deep notch between two of the teeth of the gathering wheel. The gathering pallet has risen and will strike the sprung catch (on the right) releasing the gravity arm. As the gravity arm falls the electrical contacts will meet and the gravity arm will be reset on the catch by the two large electromagnets. The action of closing the contacts sends a brief electrical impulse through the entire clock system. Advancing all the dials by one half minute and resetting the 'WT's waiting train mechanism.

The image above shows the effect of pulling on the cord which hangs inside the case on the right of the movement. A sprung lever is drawn down behind the movement which has a long pin pointing forwards. This pin directly pushes the gathering pallet continuously downwards. So, instead of the end of the pallet passing freely through the hole in the gravity arm catch it strikes the catch below the hole on every swing and releases the gravity arm. The gravity arm drops, electrical contact is made and all the mechanisms and dials in the master clock's system are now advanced every two seconds. Provided the cord is held down the system will continue to be impulsed on every pendulum swing to the right.

This is useful for advancing the clock dials for summer time. Or for resetting the system after maintenance. It should be noted that using the cord to achieve rapid advance requires some form of damping of the pendulum. Otherwise the bob will quickly build up such an arc that it will hit the case sides. I use a bath sponge to stop the bob knocking the case wall. The sponge is removed from the case after the dials have almost reach the desired time. The final adjustments to time are made by releasing the catch manually or pulling the cord briefly to "creep up" on the reference watch or clock.

Setting the master clock to the exact second is achieved by rotating the escape/gathering wheel a tooth or two by hand as necessary. One has to be very careful not to trigger an unwanted release of the gravity arm. Sometimes it helps just to lift the back click so the escape wheel is not gathered for a second or two.

It is best to stop the pendulum if the clock dials are to be set backwards by more than a few seconds. Even with an impulse 15 times as often it still takes a very long time to go "right round the dial" to make up 11 hours. Any contact programmers (for bells or factory sirens or whistles) in the time circuit will also lose their day setting if one advances the master by a full 11 hours simply to achieve an hour's retardation in the time circuit. There is also a very good chance of the impulse dials in the circuit becoming scattered in the time they show. A WT turret clock movement in the circuit will also become thoroughly confused and have to be reset. So stopping the pendulum is the best course best for retarding the time circuit.

Once a clock has been adjusted to very accurate timekeeping very small changes in rate can be made by placing small weights on the pendulum bob. A small weight placed on top of the the bob will speed up the clock by a few seconds per day depending on the weight itself. Conversely, a weight placed below the bob on the large rating nut will slow the clock slightly . Normally the clock would be adjusted to run just a few seconds slow per day. Then small weights would be added to the top of the pendulum without stopping the clock. Stopping or even touching the pendulum will almost always affect the previous rate so is best avoided. The top of the pendulum is easier to reach than the rating nut and is travelling more slowly if weights are to be added or removed.

Bronze finished, steel cased, Pulsynetic pendulum bob.

Strictly speaking a clock can be very accurate indeed but still have a slowing or gaining rate compared with standard clock time. It is the absolute steadiness of the rate which is so essential. Once the rate has been measured precisely against an accurate time signal it (the rate) can then be adjusted to match "normal" timekeeping. (i.e. neither gaining nor losing)  Usually this is done by adding small weights to the bob using tweezers to avoid touching the pendulum bob itself. Master clocks were often provided with a small wooden box containing suitable weights to fine adjust the timekeeping. Sometimes a weight tray was provided half way up the pendulum rod. Though this was not normally done with the Pulsynetic master clock. The pendulum bob top has a raised rim to stop weights from falling off too easily.

Master clocks must be bolted to a really solid wall to give their best timekeeping. If the wall should move or be subject to any vibration this will often affect the timekeeping. A solid brick or block wall is essential. Hanging a master clock from a partition wall will often stop the clock if it will run at all. The clock relies on the solid fixture for its pendulum suspension to allow it to swing steadily. Rarely will a master clock run if stood up on the floor. The movement of the Pulsynetic is provided with fixing holes so that the movement itself can be bolted very firmly to the wall rather than relying on only the case being well fixed. Screw holes near the bottom of the case are also provided to ensure the case itself is fixed firmly and exactly upright in all planes. Brass studs are provided on the clock case for this very purpose.

Uprightness for-and-aft and from side to side is essential to the accurate and reliable running of the clock. Large metal or hardwood packing spacers placed over the fixing bolts are best if the wall is not absolutely plumb. The clock must not be allowed to move relative to the wall once it is fixed. Don't take it for granted that all walls are upright. There are few bricklayer's levels which have not had a tumble from the second or third floor. I once had some new internal block walls built by a bricklayer who managed to build them 2" out of vertical thanks to his battered and mortar-encrusted level. I had became irritated by my newly hung-hall doors constantly swinging open or closed. He was quite cross when I bought a brand new four foot level to show him the quality of his workmanship. He hurled the level from the scaffolding complaining sarcastically about amateur builders not having a clue! By then it was much too late to demolish and start all over again. So take absolutely nothing for granted where the verticality of walls are concerned!

A decent, tubular aluminium level costs very little these days and is a good investment if you want the best from your master clock. Check the level's accuracy before leaving the tool shop by checking the floor and a wall carefully. Then simply reverse the whole level end for end. Or back to front on a vertical wall. Though you can turn it end for end to double check.

The bubbles should rest in exactly the same place in their glass tubes relative to the line markings despite the whole level being reversed. Don't waste your money on laser levels without checking them carefully before leaving the shop. This is rarely possible as the kit usually comes sealed in a carrying case. Levels with rotatable dials to measure slope angles are rarely accurate enough so don't go for one of those either.

A plain, rectangular, tubular four foot, aluminium level is ideal for all sort of jobs around the house and garden and will span the full height of a master clock case nicely. Gent recommended a plumb line be used to ensure the clock case was dead upright but I still prefer the long level held against both sides of the clock in turn.

Even hanging more than one clock on the same wall will often affect their timekeeping. I once had several master clocks fixed to the same workshop wall and found that two of them would stop regularly. This was simply because the wall was being moved imperceptibly by the clocks themselves as their pendulums swung in or out of unison (or phase) with each other. Being out-of-phase effectively moves the wall cyclically away from the pendulum fixing point. Resulting in a loss of power to the pendulum sufficient to bring it to a complete stop despite the regular mechanical impulsing.

When master clocks are being displayed at exhibitions and museums it is often difficult to find a suitable wall which suits the desired layout. Fixing to partition walls will often cause the clock to stop. Nobody wants to drill a solid exterior wall just to hang a master clock for a relatively brief display or exhibition. Sometimes a very large sheet of 3/4" (18mm) plywood is used to stiffen up a lightweight partition wall just for the period of the display. The clock is bolted firmly to the plywood which in turn rests on the floor for extra support and is very well screwed to the partition wall studs. Not ideal but will give a safe fixing for the length of the public display.

If you own a master clock it really deserves to be bolted to the bedrock down in some deep, dark cellar if absolute accuracy is desired. Failing this, bolting it to a thick brick or concrete wall is the next best thing. Lightweight building blocks are inferior for clock mounting as far as maximum resistance and mass are concerned. If the pendulum puts any forces into the wall then the wall must push back with equal force. (Newton's Law)

Achieving perfection has occasioned the building of massive concrete blocks into the solid rock in very deep cellars and dungeons where the finest possible timekeeping in the world was required. The cellar also had the advantage of offering a very stable temperature all year round. No doubt you will find a suitably solid location where the clock can be enjoyed and still keeps good time unless you live in a lightweight timber building.

I can still remember when the Pulsynetic master clock was being removed and sold at the main line, local railway station. (back in the 1970s) A delightful little weight driven turret clock was also sold off at the same time. My optimistically low bids were greatly exceeded as both clocks fetched a very good price indeed. The problem was trying to compete with those who love railways as well as clocks. When a clock has documented history it also gains in value well beyond the norm. It took me another 20 years to find another Pulsynetic master clock for sale. These days you can compete for them on eBay! Provided you are willing to bid against the rest of the world.

By the way: The Pulsynetic master clock is not everybody's idea of domestic bliss. They produce quite a loud clonk every half minute. If you have bolted it to a solid wall the sound will probably travel right through the structure of the building! Tolerance of a noisy clock is highly variable! I found I soon ignored my master clocks when they shared a workshop wall. They are rather like grandfather (longcase) clocks. Despite the whirring and the loud bells I quite often didn't notice half a dozen of them striking, when they were on test and I was busy repairing another clock.

Judge the sound for yourself:

Remember that Gents impulse clock systems normally run on 0.22 Amps. A minimum of 0.17A and maximum of 0.27A are tolerated. Low currents may make the system sluggish, unreliable but quieter. Higher currents can make some components rather/very noisy!

The voltage required to achieve this current will vary widely and will depend entirely on the resistance of the complete series clock circuit including any accessories. The safest method is to employ a digital multimeter and actually measure the current. The variable resistance (wire-wound potentiometer) in the master clock can then be adjusted. Or the power supply voltage increased or decreased to bring up the amperage to the correct level. Original impulse clock systems would mostly have used banks of batteries on trickle charge for reliability and independence from power cuts and variations in supply.

C7 circuit diagram kindly supplied by GV of the Netherlands.

Today's collector may use more modern batteries again on trickle or occasional charge. Fuses should be fitted on both sides of the battery to ensure greater safety. Many batteries can easily bring a connecting lead to red hot in the event of a dead short. Some clock owner use "wallwarts". Box-like mains plugs with voltage droppers and rectifiers to provide a suitable DC voltage for the clock or system. These use more power and may cost more to run over longer periods than occasional charging. They may also "droop" under load. Providing a rather sluggish reset on the master clock. Some of these small power supplies also get rather warm!

Where DC system voltages rise high enough to be a nuisance, then the clock circuits and/or accessories should be split into individual circuits. Gents components were available from the Pulsynetic range for this very purpose: From simple relays in boxes to complex, multichannel distribution boards. The avid collector can go on adding Gents "accessories" as and when they cross his path.

Click on any image for an enlargement. Back click to return to the text.



deuel said...

i wanted to ask a question.if the C7 master is responsible directly for the movement of the gent WT turrent you also discussed. and if so how? thank you

Chrisbee said...

Sorry I missed your question until now. The C7 controls the WT via a short electrical impulse every half minute. The WT runs independently from a 20Volts DC supply. Though the WT pendulum continues to swing the WT stops the drive to the clock hands for a few seconds each half minute. It does this by mechanically raising the gathering pawl from the teeth of the ratchet wheel. The WT then waits for the C7 to restart the drive via a the small electromagnet. This electromagnet releases the catch which had raised the gathering pallet and held it up. When the catch drops the WT can continue to drive the hands normally for about another half minute. It is the precise timing of the release which keeps the WT running to the same accuracy as the C7.

Juan said...

I have a large " 140 Beat Brass Bob Pendulum clock " in my office and I want more info on it. It was going to end up in the garbage and I saved it. It works but I have no idea how the 2 huge magnets work and why they are attached to leads. I placed a 1.5v battery to them and they moved and they made some noise but again I don't know what they did.
I can send you pictures.

Can you help me. Please email me at
Thank you

Chrisbee said...

Hi Juan

You have mail.

Clocking In said...

I really enjoy to read it.

Bhawana Mitra said...

How much is normally a fully working all original 1950s Gents Leicester Pulsynetic C7 worth, including original dial, hands and case, only glass broken?

Chris.B said...


I don't normally follow C7 prices so can't answer your question.

May I suggest that you do a search on eBay(UK)for C7 past winning auction bids?

A clock with a broken glass will look bad to a potential buyer. So it may not fetch such a high price as one of similar age and condition with the glass intact.

Tom Connolly said...

Is it possible to obtain a wiring diagram for a gents master clock

Chris.B said...

Hi Tom

What a good question!

I can't say I have ever seen one and the Internet doesn't help much.

One tiny image from the NAWCC forums.

As far as I recall everything is wired in series.

(Electromagnet coils, contacts, dials and the rheostat)

That said, I have never needed to rewire one.


Chris.B said...


I hope you are still following this conversation:

I have just added a circuit diagram of the Pulsynetic C7 master clock to this post.

Diagram kindly supplied by Gijs Veraart of the Netherlands.


London Lifestyle said...

Hi Chris

I bought myself a two-sided Gents station clock at the weekend which will be great in my kitchen. Discovering that the movements are slave movements I guess I could just replace them with a couple of quartz movements. But it would be much nicer to use electronics to make the slaves work, but I've no idea what it needs, or how I would do it - A-level physics being rather too long ago. I feel sure that somebody must have come up with a solution, and wonder whether it's you?! Thanks, James

Chris.B said...


Thanks for your comment.

Don't remove the original movements.

It will be much more fun to hear the slaves clunk quietly every half minute. It will also maintain the dial's value if you ever want to sell it on.

So, what you need is one of these:

"Master Clock-Pulse Generator for Slave Clocks and Slave Dials"

Do a search for this term and you'll find the eBay vendor and his recent auctions.

He auctions his impulse modules regularly.

Probably as affordable as 2 heavy duty quartz movements and then all the messing about adapting the hands to fit.