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Old 19th Aug 2020, 4:47 pm   #101
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Default Re: A phone too far ...?

Quote:
Originally Posted by Telephone Guy View Post
That aside: since I can't remove the main master socket ( B ) from the equation, the only other thing I could do to reduce overall capacitance would seem to be to take the capacitors in phones B, C and / or D out of the equation by strapping them as per Dave's instruction above.
You shouldn't have your internal capacitors in circuit anyway. They should be disconnected when you wire your telephones for plug-and-socket working, ie: the wire that goes to Pin 5 in your BT plug should go to telephone terminal 8; the wire that goes to Pin 2 in your BT plug should go to terminals 16-17-18-19, and the wire that goes to Pin 4 in your BT plug should go to terminals 5 and 6.

The 1u8 capacitor in your telephone should be disconnected - not strapped - by removing links T8 - T9 and / or links T6 - T7.

I doubt you're going to be going around in circles unless you find someone willing to chase out your wiring and put it right - including a full review of what's connected where. Whilst access to sockets and 'the unknown' may be the big issue, chasing out the wiring electrically really isn't that difficult.
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Old 19th Aug 2020, 5:06 pm   #102
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Default Re: A phone too far ...?

The trouble is that the socket that was an extra Master and is now a Slave is not correctly connected at the other end of it's cable and it isn't possible to find that and correct it. As Russell says using two capacitors — the one in the proper Master socket plus one in the extra Master socket or the one inside 'phone A (though that seems to be duff) — is asking for trouble.

I'm not suggesting you do this until people how understand the theory have commented upon it but I'm wondering if a 0.47μF capacitor in 'phone A may be large enough to allow that to ring but not big enough to upset the others.
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Old 19th Aug 2020, 6:36 pm   #103
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Default Re: A phone too far ...?

Quote:
Originally Posted by ThePillenwerfer View Post

I'm not suggesting you do this until people how understand the theory have commented upon it but I'm wondering if a 0.47μF capacitor in 'phone A may be large enough to allow that to ring but not big enough to upset the others.
That might just work! If three telephones including 3k3 resistors are currently being fed via the master LJU 1u8 capacitor and the fourth telephone including a 3k3 resistor and a 0u47 cap is connected across the A and B lines, the current in that particular telephone will be 0.8 x the current through the other three telephones, so not far off balance.

For a typical bell movement and 75V ringing signal, that would be about 7.6mA drawn by the three master-fed telephones and about 6mA drawn by the 'one-off' telephone with the 0u47 cap in cct.

The total ringing current would be about 28.6mA.

Worth a punt? The only thing is that the bell capacitor is actually part of the receiver cct on a call (although the signal goes round through the mic and ASTIC too) so the higher Z might have a mild effect on received speech.
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Old 19th Aug 2020, 7:27 pm   #104
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Default Re: A phone too far ...?

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the current in that particular telephone will be 0.8 x the current through the other three telephones, so not far off balance.
To be clear, that should read: 'through EACH of the other three telephones'.
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Old 19th Aug 2020, 7:31 pm   #105
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Default Re: A phone too far ...?

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Originally Posted by Telephone Guy View Post
I'm assuming that when you refer to the blue linecord wire, you're talking about the one that comes into the phone rather than the one that comes into the socket; when I connected the blue one that comes into the socket to T6 of the socket itself, the phone was entirely dead.
By T6 I was referring to the terminal in the telephone, not in the socket.

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Originally Posted by Telephone Guy View Post
That being said, since T5 and T6 are strapped together inside the phone, I couldn't see how repositioning the blue linecord from it's original position on T5 to T6 would make any difference ...?
It doesn't. I was just confirming that the wire should be connected to these strapped terminals. Apologies if I was unclear.

As others have said, assuming that your linecord has the standard colours, red should go to T8 (or T9 as long as it's strapped to T8), blue to T5/T6, white to T16/T17/T18/T19. Green to a spare terminal such as T15. (T11 to T14 are also available). Ensure the T6-T7 is not strapped. With this arrangement you are using the cap in the socket.

Given that you are unable to correct the wiring to the sockets themselves, the solution for balancing the ringing current between the four 'phones would seem to be to follow the suggestion of using a lower-value capacitor such as 0.47μF if you can acquire one. Using the slave socket for 'phone A, the capacitor can be connected in the socket between terminals 2 and 3, thus keeping the wiring inside 'phone A the same as all the others.

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Originally Posted by Telephone Guy View Post
As a matter of interest, I hope I've reconnected the master socket correctly; the terminals appear to be simply push-fit, which seems to work, though it doesn't seem very reliable.
Assuming these are the insulation displacement type of terminals, they make a reliable connection if the correct insertion tool is used. It is difficult to secure the wires well without an insertion tool. The best I can suggest is to push the wire down by using a small screwdriver either side of the terminal, though a tool such as the yellow one shown below can be purchased for less than £2 and should be adequate for this job. Even better is the proper tool such as the grey one, available for less than a fiver.
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Old 20th Aug 2020, 9:02 am   #106
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Default Re: A phone too far ...?

Quote:
Originally Posted by russell_w_b View Post
You shouldn't have your internal capacitors in circuit anyway. They should be disconnected when you wire your telephones for plug-and-socket working,
Is that still true even though we don't know the exact through-the-system path of the magic orange wire? - at any rate, having lost track of exactly what has or hasn't been done along the way, I've re-checked all four phones and they're all the same in this respect: T6 / T7 is unstrapped, T8 / T9 is unstrapped, and the blue line-cord wire goes to T6 ( or T5, given that T5 and T6 are strapped together ).

Quote:
Originally Posted by russell_w_b View Post
... ie: the wire that goes to Pin 5 in your BT plug should go to telephone terminal 8; the wire that goes to Pin 2 in your BT plug should go to terminals 16-17-18-19, and the wire that goes to Pin 4 in your BT plug should go to terminals 5 and 6.
Which wire goes to which pin in the BT plug, I'm not sure; up to this point I've been going mostly by colours. In the back of the phones, the green line cord goes to T12, the blue to T6, the red to T8 and the white to T18, all as per Dave's subsequent post ( I'm assuming, as per that post, that the fact of the green going to T12 as opposed to T15 is not a problem. )

Quote:
Originally Posted by russell_w_b View Post
I doubt you're going to be going around in circles unless you find someone willing to chase out your wiring and put it right - including a full review of what's connected where. Whilst access to sockets and 'the unknown' may be the big issue, chasing out the wiring electrically really isn't that difficult.
I'm sure it isn't, but for the time being we have to work on the assumption that I don't know anyone ready, willing and able to perform that task.

Quote:
Originally Posted by ThePillenwerfer View Post
The trouble is that the socket that was an extra Master and is now a Slave is not correctly connected at the other end of it's cable and it isn't possible to find that and correct it. As Russell says using two capacitors — the one in the proper Master socket plus one in the extra Master socket or the one inside 'phone A (though that seems to be duff) — is asking for trouble.
... although so far, and particularly if we're now of the view that the internal capacitor in phone A is not working, that's proven to be the only way to have phone A ringing at all ...

Quote:
Originally Posted by ThePillenwerfer View Post
I'm not suggesting you do this until people how understand the theory have commented upon it but I'm wondering if a 0.47μF capacitor in 'phone A may be large enough to allow that to ring but not big enough to upset the others.
You may be right, and the subsequent observations of Russell - who very clearly does understand the theory ( which I have to say, I don't!! ) - would suggest so. My initial thought was, how on Earth would I do this? - although, read on ...
Quote:
Originally Posted by russell_w_b View Post
Worth a punt? The only thing is that the bell capacitor is actually part of the receiver cct on a call (although the signal goes round through the mic and ASTIC too) so the higher Z might have a mild effect on received speech.
Even if this is a do-able thing, the possibility that it would have a negative effect on the volume of received speech is a major worry, given that that's a problem already ( I'm told, because of our distance from the exchange ) - in fact, one I've explored elsewhere in this forum and am still looking into. Even if I find myself able to perform the 4.7mF capacitor operation on the phones in question, if it makes the received speech any quieter than it already is, all I'm really doing is substituting one problem for another - unless anyone has any ideas on how to increase the volume of received speech without more major surgery, with or without the additional capacitors being involved.
Finally:
Quote:
Originally Posted by Dave Moll View Post
Assuming these are the insulation displacement type of terminals, they make a reliable connection if the correct insertion tool is used. It is difficult to secure the wires well without an insertion tool. The best I can suggest is to push the wire down by using a small screwdriver either side of the terminal, though a tool such as the yellow one shown below can be purchased for less than £2 and should be adequate for this job. Even better is the proper tool such as the grey one, available for less than a fiver.
... so far, the screwdriver method seems to have worked adequately, but I'll bear in mind the advice re purchasing the proper tool.

So there we are: that's how the land lies at the moment. Believe it or not, six weeks ago, I thought it would just be as simple as plugging phone A into the socket and off-we-go. Still, I suppose they thought that about the moon landing at first ...

Thanks again, all, and for anyone still reading this, by all means keep 'em coming. Surely to God something's got to work eventually.
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Old 20th Aug 2020, 9:27 am   #107
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Default Re: A phone too far ...?

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'Even if this is a do-able thing, the possibility that it would have a negative effect on the volume of received speech is a major worry, given that that's a problem already.'
I wouldn't worry. The 1u8 capacitor acts as a d.c. block for the receiver, but, as I said, received speech finds its way to the receiver via other routes. If the bell wire to BT plug pin 4 is disconnected from Terminals T5 - T6, ie: the speech route via the cap in the Master LJU which has replaced the cap in the telephone, then you can still hear the received signal just as clearly. Swapping the cap out with a 0u47 will make no perceived difference to received speech.

UK telephones are designed with economy in mind and some components are configured to have several functions!
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Old 20th Aug 2020, 10:08 am   #108
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Default Re: A phone too far ...?

Quote:
Originally Posted by Telephone Guy View Post
Quote:
Originally Posted by russell_w_b View Post
You shouldn't have your internal capacitors in circuit anyway. They should be disconnected when you wire your telephones for plug-and-socket working,
Is that still true even though we don't know the exact through-the-system path of the magic orange wire?
I think we've established that 'phones B, C and D are getting their ringing current from the (real) master socket and 'phone A from its extra master socket, so Russell is correct that none of the internal capacitors should be in circuit.

Quote:
Originally Posted by Telephone Guy View Post
Which wire goes to which pin in the BT plug, I'm not sure; up to this point I've been going mostly by colours. In the back of the phones, the green line cord goes to T12, the blue to T6, the red to T8 and the white to T18, all as per Dave's subsequent post ( I'm assuming, as per that post, that the fact of the green going to T12 as opposed to T15 is not a problem. )
Yes, stick with that rather than worrying about plug pin numbers. As to the green wire, anything between T11 and T15 is fine as these are all spare terminals in your 'phones and the wire is simply being parked to keep it out of the way.

Quote:
Originally Posted by Telephone Guy View Post
So there we are: that's how the land lies at the moment. Believe it or not, six weeks ago, I thought it would just be as simple as plugging phone A into the socket and off-we-go. Still, I suppose they thought that about the moon landing at first ...
Had your telephone sockets been correctly wired in the first place it would have been simply a matter of ensuring that all 'phones were correctly converted for plug and socket and plugging them in. The problems have arisen from the incorrect installation of socket A and having to work around that.
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Old 20th Aug 2020, 10:26 am   #109
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Default Re: A phone too far ...?

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Even if I find myself able to perform the 4.7mF capacitor operation on the phones in question...
Just to be clear: I was suggesting 0.47μF capacitor, ie nought point four seven, NOT 4.7μF — I dread to think what would happen with one of those. 0.47μF is the same as 470nF. Different makers/suppliers use different terms. One may also be marked 474.

With all respect to Dave I'd fit it in the 'phone between T6 and T9 as getting one into the IDC connectors inside the socket may be a challenge as the wires on the cap could well be too thick or thin. You'd just have to remember to remove it if you move that 'phone to a different socket and fit it in any that replaced it.
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Old 20th Aug 2020, 11:01 am   #110
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Default Re: A phone too far ...?

Sorry, I hadn't mentioned that the slave socket in question (to which I suggested the capacitor be added) has screw terminals, not IDC. It is the "master" that is IDC. Having the capacitor in the socket avoids the problem of swapping 'phones between sockets.

I have sent TG a PM with a possible source of 0.47μF capacitors in case he decides to go down this route - which seems to be the only feasible work-around for the existing socket setup.
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Old 20th Aug 2020, 11:22 am   #111
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Default Re: A phone too far ...?

Thanks for the clarification Dave. I agree that the socket is the best place for a capacitor.
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Old 20th Aug 2020, 11:47 am   #112
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Default Re: A phone too far ...?

Having looked inside that slave socket's twin, there is an even neater way of making up the required pseudo-master, subject to the availability of soldering, and that it is to unscrew the circuit board from the faceplate and solder a 0.47μF in the position marked "C1".
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Old 20th Aug 2020, 12:33 pm   #113
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The problems have arisen from the incorrect installation of socket A and having to work around that.
Probably academic now, but presumably the problem lies in a combination of the original installation of socket A as a master rather than a slave AND the fact that the internal capacitor in phone A evidently isn't working? I digress ...

I don't really want to be venturing into soldering-iron territory if it can be avoided, but if the new capacitor can be inserted into the screw terminals in the slave socket, or even at a pinch between T6 and T9 of the phone, that sounds like a viable course of action, and from what I'm gathering, the rest of you would agree. As regards my having incorrectly quoted the capacitance value, once again, my bad ... I'm taking as read that the PM Dave has kindly sent me refers to the correct value!

Just to make sure I've got this right:

As regards phone A, if I've understood correctly, the plan would be to swap the socket back to the slave that Dave supplied and then insert the new 0.47mF capacitor between T6 and T9 of the phone ( or in the slave socket ... between which and which terminals, again ...? ). I assume all four 3.3k resistors should be left in place in each of the four phones and all strapping should remain as it currently is, and none of the other three phones require additional capacitors since ( we believe ) they're all being rung from the capacitor in the main master socket ( socket C ).

Does this sound right? - and have I understood correctly that if I insert the capacitor into slave socket A rather than into the phone itself, all the phones would then, theoretically, be interchangeable ( not that I currently have any intention of changing any of them round )?
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Old 20th Aug 2020, 1:16 pm   #114
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Default Re: A phone too far ...?

The assumptions in your final two paragraphs appear to be correct. If you put the new capacitor in the socket it need connecting to terminals 2 and 3.

You have three 'phones in full working order that appear to be connected to correctly wired sockets. The duff capacitor in 'phone A shouldn't matter but has only become relevant as the socket it is connected to isn't correctly wired. The fundamental fault is the other end of the cable going to the extra Master socket (as was) not being properly installed.
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Old 20th Aug 2020, 1:59 pm   #115
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Default Re: A phone too far ...?

I've just tried connecting a 746 with a 0.47uF capacitor between T8 (red) directly to T6 and T5; 3k3 resistor T5 - T4; break between T6 - T7 and break between T8 - T9. Blue wire not connected and taped up. Effectively what you're trying to achieve but with the cap in the slave LJU.

It rings perfectly. The only subjective effect is a v-e-r-y tiny reduction in side tone: barely noticeable.
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Old 20th Aug 2020, 2:21 pm   #116
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Default Re: A phone too far ...?

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Quote:
Originally Posted by Dave Moll View Post
The problems have arisen from the incorrect installation of socket A and having to work around that.
Probably academic now, but presumably the problem lies in a combination of the original installation of socket A as a master rather than a slave AND the fact that the internal capacitor in phone A evidently isn't working? I digress ...
The state of the capacitor in 'phone A can be ignored if we're not using it - as is the case with a converted telephone.

Quote:
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I don't really want to be venturing into soldering-iron territory if it can be avoided, but if the new capacitor can be inserted into the screw terminals in the slave socket, or even at a pinch between T6 and T9 of the phone, that sounds like a viable course of action, and from what I'm gathering, the rest of you would agree.

Just to make sure I've got this right:

As regards phone A, if I've understood correctly, the plan would be to swap the socket back to the slave that Dave supplied and then insert the new 0.47mF capacitor between T6 and T9 of the phone ( or in the slave socket ... between which and which terminals, again ...? ).
I was assuming you wouldn't want to start soldering. As to the socket terminals, the capacitor goes between 2 and 3 - with the incoming pair still to 2 and 5 as before.

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I assume all four 3.3k resistors should be left in place in each of the four phones and all strapping should remain as it currently is, and none of the other three phones require additional capacitors since ( we believe ) they're all being rung from the capacitor in the main master socket ( socket C ).

Does this sound right? - and have I understood correctly that if I insert the capacitor into slave socket A rather than into the phone itself, all the phones would then, theoretically, be interchangeable ( not that I currently have any intention of changing any of them round )?
As others have said, this sounds an accurate summary.
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Old 20th Aug 2020, 2:31 pm   #117
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Quote:
Originally Posted by ThePillenwerfer View Post

Just to be clear: I was suggesting 0.47μF capacitor, ie nought point four seven, NOT 4.7μF — I dread to think what would happen with one of those. .
What would happen is that you'd draw a reasonable* 31.34mA typically from the line, with each of the three 'master-fed' instruments drawing 7.55mA leading and the 4.7uF-fed 'slave' instrument drawing 14.61mA lagging.

* 'Reasonable' being commensurate with the 32.7 mA drawn by ONE unconverted 746 having a REN of 4. Of course, there'd be a greater imbalance of ringing currents with each 'master'-fed telephone drawing about half the current of the slave 'n' modified cap one.

Might work on a short line!
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Old 20th Aug 2020, 2:33 pm   #118
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Default Re: A phone too far ...?

Firstly, thank you for your indulgence. Secondly: is 'side tone' the same as 'received speech volume'? - or if not, what is it ( in layman's terms! )?

Assuming 'side tone' does translate as above, does this affect only the phone in question, or ( in my case ) all four phones in the circuit? Other than that, is your wiring pattern ( Russell ) slightly different than previously suggested? Shouldn't the incoming blue wire be connected to T6? - and doesn't the 0.47mF capacitor go between T6 and T9? Don't get me wrong - I'm not by any means attempting to second-guess you - but just want to be sure I do it right, when I do it. I don't know if this has anything to do with the fact of you testing it on a 746 ( thank you again, by the way ) and me using a 782? - and last but not least, would you expect that the fact of me having the other three phones in the circuit would have any bearing on the result?
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Old 20th Aug 2020, 2:45 pm   #119
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Default Re: A phone too far ...?

Side tone is the sound of your own voice in the ear-piece, not the other person.

I honestly can't see it being a problem as the volume was OK with two 1.8μF capacitors in two master sockets so reducing one of those to 0.47μF can only help in that regard.

In fact in ye olde days the ringing capacitor was 2μF so a 1.8μF plus a 0.47μF won't be much above that. In fact the old ones were only 2μF IN THEORY as they would be more or less in practise. I don't know the tolerance they were made to but I'd expect it to be twenty per cent so your proposed new total of 2.27μF should be fine.
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Old 20th Aug 2020, 2:47 pm   #120
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Firstly, thank you for your indulgence. Secondly: is 'side tone' the same as 'received speech volume'? - or if not, what is it ( in layman's terms! )?

Assuming 'side tone' does translate as above, does this affect only the phone in question, or ( in my case ) all four phones in the circuit?
Side tone is your own voice you hear in the receiver. incoming speech from other parties not affected.

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Other than that, is your wiring pattern ( Russell ) slightly different than previously suggested?
No. My experimental rig was how telephones USED to be wired with the cap in the telephone and just two line wires. All the blue wire does to T6 is 'build the capacitor out' of the telephone into the master box. Electrically it is identical. I tried it like this as I don't have a socket to play with and had to use the telephone only.

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I don't know if this has anything to do with the fact of you testing it on a 746 ( thank you again, by the way ) and me using a 782?
No difference: the 782 has MF dialling but speech / ringing is identical to 746.

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and last but not least, would you expect that the fact of me having the other three phones in the circuit would have any bearing on the result?
Shouldn't do. But there's only one way to find out!
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