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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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20th Aug 2020, 3:14 pm | #121 |
Tetrode
Join Date: Jan 2020
Location: Canterbury, Kent, UK.
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Re: A phone too far ...?
I understand now why it's called 'side tone' ... sounds to me like a reduction in that would actually be a good thing ...?
But other than that, as you say, the proof of the pudding ... I've ordered the capacitors and will report back in due course. They're not expected to arrive until Monday or Tuesday, so sometime after that if there are no other developments in the meantime! |
20th Aug 2020, 4:17 pm | #122 |
Dekatron
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Location: Greater Manchester, UK.
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Re: A phone too far ...?
It explains "side", but what about "tone"?
The answer is it goes back to telegraphy operators. It is helpful to hear your own (Morse code) keying as a tone in your headphones when you are sending.
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24th Aug 2020, 2:25 pm | #123 |
Tetrode
Join Date: Jan 2020
Location: Canterbury, Kent, UK.
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Re: A phone too far ...?
Okay, here it is: I've connected the capacitor in socket A as instructed. The result is that all four phones are ringing at about 75% of full strength, although on the plus side, all four of them seem to be ringing to about the same degree. In case '75% of full strength' isn't very clear, the nearest description I can give - and it isn't meant to be literal - is if each bell were receiving around 75% of the power it needs to ring at what would be considered 'normal volume' for that bell.
On the one hand, I feel instinctively that there must be a way to get all four phones ringing at 100%. On the other hand, that's instinctive rather than scientific, and it may well also be the case that the work required to get that extra 25% might be more than is feasible, given all the circumstances. As always, I'd be interested to hear any and all observations. |
24th Aug 2020, 3:52 pm | #124 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
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Re: A phone too far ...?
There is a way to get them to all ring properly: sort out the wiring. Anything else is always going to be bodge and not likely to work perfectly. As that isn't possible you've probably got the best you can hope for.
Unless you have a very big house or hearing problems I'd have thought that four 'phones ringing at seventy-five per cent would be plenty loud enough. |
24th Aug 2020, 4:44 pm | #125 | |
Dekatron
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Location: Penrith, Cumbria, UK.
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Re: A phone too far ...?
Quote:
Trouble is, your line limitation (the length and resistance of it) mean you only have so much current to deal with and it's up to you to decide where to put it. The reduction of REN by inserting a 3k3 resistor to a ringer circuit using a 1 kilohm bell movement was always a codge and was originally designed for Trimphone electronic ringers, not magneto bells. But it works in most cases. You have to remember that a type 59A bell movement as you have in your telephones is designed to give maximum sound output when drawing around 20 - 30mA. That's per bell. You have several options:- Try to source some 4k bell-movements, which are a direct replacement for the 1k bell movements currently in your telephones. The 4k bell movement was fitted to bell instruments to give a REN of 1 and was the official modification. Look out for a small PABX which would allow you to use all your telephones and would supply a suitable magnitude of ringing current. You'd need to modify your wiring to do this, I suspect. Get your wiring sorted. You might enjoy a slight increase in bell volume if you have one 1u8 capacitor in series with four modified bells in parallel. But it won't be much. You could go 'non-standard' and wire all your bells in series as they used to be wired before plugs and sockets and liberalisation but, again, this would mean you getting at the wiring.
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24th Aug 2020, 7:19 pm | #126 |
Dekatron
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Re: A phone too far ...?
As a matter of interest, how many bells wired in series as originally intended are allowed?
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24th Aug 2020, 7:54 pm | #127 |
Dekatron
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Re: A phone too far ...?
Six.
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24th Aug 2020, 8:10 pm | #128 |
Dekatron
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Re: A phone too far ...?
Talking of series-connected bells, two 1k 59A bell-movements in series hits the 'sweet spot' and almost resonates with the 1u8 capacitor: something like a 10 degree phase-angle or thereabouts.
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Regds, Russell W. B. G4YLI. |
24th Aug 2020, 11:35 pm | #129 |
Dekatron
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Re: A phone too far ...?
Interesting, thanks Russell.
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25th Aug 2020, 7:38 am | #130 |
Dekatron
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Re: A phone too far ...?
You're welcome. Bill.
I once considered using the plug-and socket arrangement to do a series connection with an extension bell (a bit like the four-pole jacks you sometimes got on the 'old' plug-and socket plan system where a bellset was always hard wired) and it would work, but, of course,it makes things non standard and unique to the house. But, if you're stuck, it's another way to decrease the REN without wasteful resistors. I suppose you could wire a 'traditional' system of series-bell coonnected telephones via one plug at the master LJU if you wished.
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25th Aug 2020, 12:51 pm | #131 | |||
Tetrode
Join Date: Jan 2020
Location: Canterbury, Kent, UK.
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Re: A phone too far ...?
Quote:
Quote:
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Since it appears that all the options that don't involve access and surgery to the wiring have been exhausted - and since, as mentioned above, 75% on all four phones is an acceptable result and probably the best it was ever going to be, given the circumstances - I think I have to take that as a win and move on! My thanks to everyone for their indulgence, help, suggestions, and in Dave's case, practical assistance, in what I never dreamed would become the epic it has. If anyone else wishes to ruminate, I will continue to watch with interest, but unless anyone's got a magic wand, I think I'm pretty much done! Thanks to you all once again. |
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25th Aug 2020, 1:43 pm | #132 |
Dekatron
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Re: A phone too far ...?
Well, it's been interesting! Changing bell-bobbins isn't that difficult though you would need a soldering iron. Worth keeping an eye out, even if it means doing one phone at a time. You might even come by a telephone that has them fitted.
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25th Aug 2020, 3:22 pm | #133 |
Octode
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Re: A phone too far ...?
Do you happen to know the size of the wire, Russell? I've got a couple of o/c 500Ω ones that I'd like to re-wind at 2000Ω.
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25th Aug 2020, 4:30 pm | #134 |
Dekatron
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Re: A phone too far ...?
Not for the 2k bobbins, I'm afraid. However... It's 0.044" diameter for the 500 Ohm ones. If you look at a GEC telephone made at Newton Aycliffe (stamped GEN) they've very kindly put the wire diameter AND the number of turns on the bell bobbins! Other manufacturers may have done the same.
And it checks out. I have both metric and imperial sizes printed on different 59A bells, and I worked out the length of the wire that gives 500 Ohms and the number of turns (average diameter method) that fits the dimensions on the bobbin. I have one telephone at home with a 4k bell-movement in it, so I'll take a look and pass on any details, if they're written down. If it's any help - you'll need to know the core material, length and diameter for this - the inductance of a single bobbin is around 27.5H (I measured 26 using 'real' current). I think a 500 Ohm bell movement is about 4.5 H outside the magnetic circuit.
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Regds, Russell W. B. G4YLI. Last edited by russell_w_b; 25th Aug 2020 at 4:37 pm. Reason: Inductance details of a Type 59A single bell bobbin. |
25th Aug 2020, 6:04 pm | #135 |
Dekatron
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Re: A phone too far ...?
I looked at my 2000 Ohm bobbins, but nooooo...
However... Assuming all ironwork, permeability equal, then the inductance is proportional to the number of turns squared. So a 500 Ohm bobbin of 4.5 Henries (say) has 8,750 turns of 0.044" wire on it. Then a bobbin with an inductance of 27.5 Henries will have: (sq rt (27.5/4.5)) x 8750 = 21,631 turns on it. Now we know the bobbins are the same physical size, so it's simply a matter of working out what diameter wire will give you the same cross-sectional area as that occupied by the wire on a 500 Ohm bobbin.
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25th Aug 2020, 6:31 pm | #136 |
Octode
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Re: A phone too far ...?
Thanks for looking.
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25th Aug 2020, 6:32 pm | #137 |
Dekatron
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Re: A phone too far ...?
By proportion, it would be 0.0178", so try 25AWG: 0.0179". It's a good starting point anyway, if a lot of work!
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Regds, Russell W. B. G4YLI. |
25th Aug 2020, 6:46 pm | #138 |
Octode
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Re: A phone too far ...?
At least I can see 25AWG.
Thanks again. |
25th Aug 2020, 8:44 pm | #139 |
Dekatron
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Re: A phone too far ...?
Sorry- made a right horlicks of that. It's 0.0044", not 0.044" (Specsavers calls...). Don't dash out and buy any 25AWG just yet. I just checked on the other bell which converts near enough at 0.112mm. This is for a 500 Ohm bobbin, remember.
I'll look up some metric wire tables. AWG seem to vary! And it's the CSA we're interested in - not the diameter. It'll be very thin wire!
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Regds, Russell W. B. G4YLI. Last edited by russell_w_b; 25th Aug 2020 at 9:02 pm. |
25th Aug 2020, 9:13 pm | #140 |
Octode
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Re: A phone too far ...?
0.0044" is 41SWG.
I thought there was something amiss as 0.044" is over a millimetre and I knew it wasn't that thick. Looking at the ohms per meter figures I'd have needed nine miles to get to 2000Ω! |