Gents turret slave

Here is a late model turret slave on eBay(UK)

I have done my best with the images having enlarged, sharpened and increased both gamma and contrast. The original images were undersized and probably taken with flash.

A soft wash of daylight (overcast or not direct sunshine) against a plain (uncluttered) neutral density background is far better for technical images.

Packaging cardboard makes an excellent background since it is neutral in density and colour and reflective without gloss. It is also readily available in all sizes. Often completely free of charge at supermarkets and shops.

Larger images are far easier to examine for fine detail and capable of much greater enlargement.

This slave is unusual for having only 60 teeth on the impulse wheel. This would need a short, low voltage, drive impulse at only one minute intervals. An unusual requirement where most master clocks impulse at 30 second intervals. NEVER MAINS ELECTRICITY! The unit looks to be in excellent condition with only minor corrosion on the hour sleeve.

Later master clocks offered impulses at 1 minute intervals. An irony considering that 1/2 minute impulse dials are showing the correct time, more accurately for most of the time. (The hands move very briefly and then remain still until the next short impulse arrives)  It follows that a 1-minute activated dial is only showing the correct time for 1 second in 60.

The hour pipe sleeve will just reach through a single skin brick wall. Though the dial itself would probably need to be thin and flat to allow the hands to turn freely.

Turret slave dials can be very reliable when the hands are not too large and reasonably sheltered. Problems arose when they were asked to drive the hands of a large, very exposed dial to save money.

Unfortunately placing the dial and hands behind glass makes reading the time very difficult indeed when the glass is reflecting the open sky.

These later Gents slave units were made with conservation of materials in mind.

Brackets would be bent as tabs from the solid sheet rather than adding a bolt on component.

The double-locking mechanism holds the hands quite still against external forces until the impulse frees the action and moves the hands on.

The hands would still need to be light and balanced to avoid the slave having to work beyond its physical limitations.

The actual drive to the hands is by means of a spring. The spring is drawn back by the electromagnet(s) armature. Then the impulse wheel is driven by a pawl pushing a tooth forwards on the rim as the spring gives up its applied tension.

Since the electromagnet only receives a very short impulse and has limited drawing power this, in turn, handicaps the maximum potential strength of the drive spring. Larger slaves used twin electromagnets to obtain more power.
They could then use stronger drive springs to push against larger impulse wheels for more leverage and hand control.

Should the clock hands be subject to icing, perching birds or strong winds the slave's drive mechanism might stall temporarily. Many turret slave clocks were placed behind glass to avoid such problems. Or used under cover such as in train and bus stations, large factory buildings, etc.

Where larger, exposed dials were required the Waiting Train mechanism was an incredibly powerful but far more expensive option. For modest dial sizes the turret slave was a relatively inexpensive option. After all, the smaller, office-sized, slave dials were made in their millions with excellent reliability.

This interesting item sold for £83.57 after 16 bids.

Click on any image for an enlargement.


Nicholas said...


I was fascinated to come across your blog about this movement, because I was the lucky high bidder in the auction!

I'm intrigued to know it's a Gents.

The seller told was kind enough to tell me the following: "I bought the movement at Brunel Clock Fair. The dealer had several in a box and had all come from , I think, a railway station. He had all the hands there, and they were aluminium counter-balanced and the minute hands were about 20 inches long. That means a dial of 3 ft 6 to 4 ft. I never got the hands as I was going to use it indoors. I can't be any more precise than that. I don't know what voltage the solenoid needs, but it must be more than the 5 volts or so on Master clocks, as it doesn't actuate at that voltage."

When do you suppose it dates from?

Do you think it could be used in a non-covered situation, or would water ingress be a problem?

Many thanks,


Nicholas said...
This comment has been removed by a blog administrator.
Chris.B said...

Hi Nick

Congratulations on your interesting auction win!

When you say you are new to this do your mean computers, blog comments or electrical horology?

Do you have a master clock of any kind? Any knowledge or reference books on the subject? Are you a member of any of the online electric clock forums?

I can only guess at the age but Gilbert/Gijs, the [Dutch] Gents expert, shows one on his Pulsynetic website and has dated it as 1950. Which rather surprised me. I thought it would be later.

Do you have a digital multimeter to measure the resistance of the coil? Assuming that your slave was used in a normal Gents' series impulse clock circuit it would need 0.22A to drive the circuit.

Total resistance of clock circuit x 0.22 = voltage required.

Slave clocks had different coil resistances depending on size:
12" dial = 4 Ohms.
12-18" = 6 Ohms
18-24" = 8 Ohms
30" = 30 Ohms
36" = 35 Ohms etc.

Station clock dials would normally be under cover so they were not designed to resist wet weather.

Your slave movement is slightly unusual for having only 60 teeth on the impulse wheel. This means it needs a short electric pulse only once a minute. Unless you have a master clock, which can provide such an impulse, you are going to need to be inventive.

This message is getting longer by the minute: I don't want to swamp you with information. Though I can provide more information, reference sources, contacts etc if you like. Just ask.

It might be better to take to direct email contact if you want to share images.

chris.b [at]

Better images would certainly be nice. Can I just ask that you use overcast daylight or shade and a very plain background? Cardboard, hardboard or a concrete paving slab all work very well. Indoor flash and bright sunlight can sometimes make poor lighting for technical images.


Nicholas said...

Hello Chris, and apologies for the slow reply.

I'm new to blogs, but fortunately, reasonably au fait with computers and electric horology.

Interesting re. the supposed date of 1950. I too thought it would be later not least because of the blue/brown colour coding of the flex to the coil which seems to be original.

Point taken about weather protection, so I might have to revise my plans! I wonder whether O-rings could be used to provide a degree of rainproofing.

I do have a c.1950 Synchronome master which gives 30s impulses, as well as Piexx and Mark Lines electronic slave drivers which I think can provide 1-minute outputs. I've also successfully built a DIY unit from 4000-series CMOS chips to drive my Gledhill-Brook time recorder, so I should be OK in this respect.

DC resistance of the coil seems to be ~47R, albeit shunted (I think) by a 1K5 resistor. So maybe a 4' dial was indeed fitted as the seller suggested.

I will definitely send you some better pics when it stops raining!

Thank you again,