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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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19th Aug 2020, 4:47 pm | #101 | |
Dekatron
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Re: A phone too far ...?
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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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Regds, Russell W. B. G4YLI. |
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19th Aug 2020, 5:06 pm | #102 |
Octode
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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. |
19th Aug 2020, 6:36 pm | #103 | |
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Re: A phone too far ...?
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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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19th Aug 2020, 7:27 pm | #104 |
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Re: A phone too far ...?
To be clear, that should read: 'through EACH of the other three telephones'.
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19th Aug 2020, 7:31 pm | #105 | ||
Dekatron
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Re: A phone too far ...?
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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. 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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Mending is better than Ending (cf Brave New World by Aldous Huxley) Last edited by Dave Moll; 19th Aug 2020 at 7:35 pm. Reason: replace duff image |
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20th Aug 2020, 9:02 am | #106 | |||||||
Tetrode
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Re: A phone too far ...?
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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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20th Aug 2020, 9:27 am | #107 | |
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Re: A phone too far ...?
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UK telephones are designed with economy in mind and some components are configured to have several functions!
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20th Aug 2020, 10:08 am | #108 | ||
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Re: A phone too far ...?
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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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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
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20th Aug 2020, 10:26 am | #109 | |
Octode
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Re: A phone too far ...?
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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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20th Aug 2020, 11:01 am | #110 |
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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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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
20th Aug 2020, 11:22 am | #111 |
Octode
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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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20th Aug 2020, 11:47 am | #112 |
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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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20th Aug 2020, 12:33 pm | #113 | |
Tetrode
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Re: A phone too far ...?
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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. 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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20th Aug 2020, 1:16 pm | #114 |
Octode
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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. |
20th Aug 2020, 1:59 pm | #115 |
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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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20th Aug 2020, 2:21 pm | #116 | |||
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Re: A phone too far ...?
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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
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20th Aug 2020, 2:31 pm | #117 | |
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Re: A phone too far ...?
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* '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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20th Aug 2020, 2:33 pm | #118 |
Tetrode
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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? |
20th Aug 2020, 2:45 pm | #119 |
Octode
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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. |
20th Aug 2020, 2:47 pm | #120 | |||
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Re: A phone too far ...?
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Shouldn't do. But there's only one way to find out!
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