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Old 21st Aug 2022, 1:38 pm   #1
Voxophone
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Default Gents master clock - transistor relay?

Hi all,

I've come across a Gents master clock (dated Oct 1962) which has an additional transistor-based PCB installed in it. Does anyone know if this is an official component or some kind of retrofit, and what it might gave been used for?

I'm aware of how the standard Gents master/slave clock system works, and the only reason I could imagine a relay being needed might be to drive more slave dials above a certain limit.

Cheers,

Liam
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Old 21st Aug 2022, 4:17 pm   #2
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Default Re: Gents master clock - transistor relay?

Liam,
Can we assume that the master clock is a standard Pulsynetic, with 30 second impulses designed to drive series-connected slave dials in a current-loop?

Gents produced transistor PCBs for various purposes, for example to drive series loops instead of relay drives, to drive 60 second slaves, to drive 24v slaves with either unipolar or alternating-polarity impulses. Just about anything!

We need more details, please.

Andy
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Old 22nd Aug 2022, 1:42 pm   #3
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Default Re: Gents master clock - transistor relay?

Thanks Andy. Sounds like there could be a few reasons for having the relay.

I've attached some pictures below.

Cheers,

Liam
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Old 22nd Aug 2022, 3:37 pm   #4
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Default Re: Gents master clock - transistor relay?

It doesn't look too difficult to draw out the circuit of that PCB.

Andy
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Old 22nd Aug 2022, 3:42 pm   #5
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Default Re: Gents master clock - transistor relay?

What are the extra contacts below the standard mechanism? They could be to drive a seconds hand or alternating polarity slaves via the PCB. I think you need to draw out the full circuit!

Andy
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Old 22nd Aug 2022, 4:40 pm   #6
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Default Re: Gents master clock - transistor relay?

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Originally Posted by M0FYA Andy View Post
What are the extra contacts below the standard mechanism? They could be to drive a seconds hand or alternating polarity slaves via the PCB. I think you need to draw out the full circuit!

Andy
Agreed, my money is on alternate polarity seconds drive for slaves as it has the seconds contacts on the pendulum crutch.
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Old 22nd Aug 2022, 11:19 pm   #7
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Default Re: Gents master clock - transistor relay?

It does appear to be a proper Gents board . I have seen a similar one operating on 50 volt with a one second alternative polarity system.
I take it the separate contact below the mechanism is connected directly to the PC board and dosnt go through the main clock wiring .
I do have a transistorised Gents relay for a normal 30sec system and it is just that basically a relay , capacitor and a couple resistors in a metal box.Nothing like your board . I hope you don’t mind if I pass your photos on to someone I know who’s not on here but probably knows more than me .
Alway interesting to find things a little different Andy
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Old 23rd Aug 2022, 12:49 pm   #8
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Default Re: Gents master clock - transistor relay?

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It does appear to be a proper Gents board . I have seen a similar one operating on 50 volt with a one second alternative polarity system.
I take it the separate contact below the mechanism is connected directly to the PC board and dosnt go through the main clock wiring .
I do have a transistorised Gents relay for a normal 30sec system and it is just that basically a relay , capacitor and a couple resistors in a metal box.Nothing like your board . I hope you don’t mind if I pass your photos on to someone I know who’s not on here but probably knows more than me .
Alway interesting to find things a little different Andy
No problem with you passing the photos on . It would be good to get to the bottom of this.

I suppose the thing I'm struggling to get my head around is why transistors would be needed at all for something like this. The basic 30 second Pulsynetic system works on a purely electromechanical basis. I can't think why driving a separate system on a different voltage would need more than another set of contacts switching a separate circuit.

Liam
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Old 23rd Aug 2022, 1:43 pm   #9
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Default Re: Gents master clock - transistor relay?

We had an ageing Gents system where I once worked and my boss put some sort of relay follower on it because the contacts were worn and unreliable.

He later superceded the whole thing with a TTL counter arrangement coming off the mains - more than accurate enough for our purposes.
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Old 23rd Aug 2022, 2:17 pm   #10
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Default Re: Gents master clock - transistor relay?

This paper may answer your question 'Why Transistors'?

Sorry for the quality of the pdf, it's all I have.

Andy
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Old 23rd Aug 2022, 2:38 pm   #11
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Default Re: Gents master clock - transistor relay?

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Originally Posted by M0FYA Andy View Post
This paper may answer your question 'Why Transistors'?

Sorry for the quality of the pdf, it's all I have.

Andy
Very interesting, thanks for posting. So it could be the case that the relays replace the functionality of some of the mechanical contacts.
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Old 23rd Aug 2022, 10:49 pm   #12
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Default Re: Gents master clock - transistor relay?

I’m not sure but looking at the photo. It looks like no wires are connected the the variable resistor. Is this correct. If that’s correct I would assume all slaves must go through the circuit board .
I have passed your pictures on to someone who’s probably a bit more knowledgeable on these circuits.
In his opinion . He called it a card not a circuit board. 2 versions were made a 24 volt and a 50 volt. 50 volt was for longer runs with more clocks . Probably 4ohm wired in series. But still regulated to about 220ohm.
Apparently some places used the alternative polarity clocks , ie hospitals and bbc etc . As when new the slaves were much more quiet than the traditional clocks.
I believe there was a connection with Plessey on the electronic stuff.
Apparently the transistors often fail and are getting a little hard to come by.
I probably have a circuit diagram for personal use only if you are really stuck. If not for this circuit board but a very similar one.
Andy
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Old 25th Aug 2022, 1:04 pm   #13
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Default Re: Gents master clock - transistor relay?

Quote:
Originally Posted by bionicmerlin View Post
I’m not sure but looking at the photo. It looks like no wires are connected the the variable resistor. Is this correct. If that’s correct I would assume all slaves must go through the circuit board .
I have passed your pictures on to someone who’s probably a bit more knowledgeable on these circuits.
In his opinion . He called it a card not a circuit board. 2 versions were made a 24 volt and a 50 volt. 50 volt was for longer runs with more clocks . Probably 4ohm wired in series. But still regulated to about 220ohm.
Apparently some places used the alternative polarity clocks , ie hospitals and bbc etc . As when new the slaves were much more quiet than the traditional clocks.
I believe there was a connection with Plessey on the electronic stuff.
Apparently the transistors often fail and are getting a little hard to come by.
I probably have a circuit diagram for personal use only if you are really stuck. If not for this circuit board but a very similar one.
Andy
Thanks Andy,

From looking more closely at the extra set of contacts that are actuated by the pendulum, they close on each half cycle of the pendulm (i.e. once when it swings left and again when it swings right).

From reading online, it sounds as if standard 1 second slave dials use a contact which closes only once per full cycle of the pendulm, whereas the type I have would be used for alternate polarity slaves.

I'll have a go at tracing the circuit through the PCB and see what this shows. I'm guessing it will need to provide some way of inverting the polarity of one of the pulses for the alternate polarity slaves to work.

Cheers,

Liam
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Old 26th Aug 2022, 11:03 am   #14
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Default Re: Gents master clock - transistor relay?

Quote:
Originally Posted by Voxophone View Post
Quote:
Originally Posted by bionicmerlin View Post
I’m not sure but looking at the photo. It looks like no wires are connected the the variable resistor. Is this correct. If that’s correct I would assume all slaves must go through the circuit board .
I have passed your pictures on to someone who’s probably a bit more knowledgeable on these circuits.
In his opinion . He called it a card not a circuit board. 2 versions were made a 24 volt and a 50 volt. 50 volt was for longer runs with more clocks . Probably 4ohm wired in series. But still regulated to about 220ohm.
Apparently some places used the alternative polarity clocks , ie hospitals and bbc etc . As when new the slaves were much more quiet than the traditional clocks.
I believe there was a connection with Plessey on the electronic stuff.
Apparently the transistors often fail and are getting a little hard to come by.
I probably have a circuit diagram for personal use only if you are really stuck. If not for this circuit board but a very similar one.
Andy
Thanks Andy,

From looking more closely at the extra set of contacts that are actuated by the pendulum, they close on each half cycle of the pendulm (i.e. once when it swings left and again when it swings right).

From reading online, it sounds as if standard 1 second slave dials use a contact which closes only once per full cycle of the pendulm, whereas the type I have would be used for alternate polarity slaves.

I'll have a go at tracing the circuit through the PCB and see what this shows. I'm guessing it will need to provide some way of inverting the polarity of one of the pulses for the alternate polarity slaves to work.


Cheers,

Liam
Liam,
You are correct, the 'ratchet' type seconds slaves use a pendulum switch that momentarily closes as it passes through '0' position each swing, whereas what you have gives a closed contact when in one direction and and open contact in the other. The circuit will be used to covert the contact state into an alternate polarity to drive C400 slave movements. These were a lot quieter in operation than 1 second ratchet type they are loud!
Hope you make sense of the PCB it won't be hard to draw out and it will make sense then
As said earlier by Andy, if the rheostat is not connected, the PCBs may also provide 30 second pulses to drive alternate polarity 30 second slaves on a 24v parallel circuit. These are quieter and more suited to a domestic situation, I have a mixture of both systems, you soon get used to it.
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