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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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27th Mar 2015, 3:19 am | #1 |
Retired Dormant Member
Join Date: Feb 2015
Location: Minnesota, USA.
Posts: 16
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Early Telephone with no induction coil?
I hope that someone here can help me with question that I have. I have an early phone that has no need of an induction coil. All it contains is the housing, the switch hook, and the receiver. There is no ringer. It works fine, loud and clear! I have looked within and find no components that differ from other similar sets with induction coils. I have never seen one without such a coil. I also have a vintage telephonist headset that terminates in a 2 prong plug instead of the 4 conductor type. I see nothing different with this headset except for the plug. When I apply battery to both the subset and the headset both transmitters an receivers work fine. Obvious there must be some different sort of transmitter or receiver in either sets that eliminate the need for an induction coil. Thank you for taking the time to respond, dave
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27th Mar 2015, 7:17 am | #2 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Early Telephone with no induction coil?
Yes and no.
It is depending on the type of telephone. Some early telephones had a special receiver with integrated induction coil. (more than 2 wires to the receiver). More likely it may be one of the phones using a separate sub-set containing induction coil, ringer, capacitor (condenser) and sometimes an inductor (generator). Pictures, and information of make and model may help us to be more specific. This has been discussed in another forum: http://www.classicrotaryphones.com/forum The book "Old Time Telephones!" by Ralph Meyer may solve "all your problems" dsk |
27th Apr 2015, 8:30 pm | #3 |
Hexode
Join Date: Sep 2012
Location: Yorkshire, UK.
Posts: 329
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Re: Early Telephone with no induction coil?
My GPO 150 Candlestick phone from what I remember has no induction coil, I bought it off eBay a few months back. I wasn't even expecting it to work as I only paid like £80 for it, so I extremely surprised to see that it came with a phone plug already attached plugged it in and it worked. No ring obviously, but other than that I can dial out and make calls etc.
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27th Apr 2015, 9:12 pm | #4 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: Early Telephone with no induction coil?
The induction coil is inside the bellset, which was a separate unit, presumably missing on yours.
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7th May 2015, 5:49 pm | #5 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Early Telephone with no induction coil?
It is possible for a telephone to work without an induction coil, either by design or bodgery.
I've got a horrible Telephone Rentals thing which is designed without one. - Joe |
7th May 2015, 6:29 pm | #6 |
Hexode
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 444
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Re: Early Telephone with no induction coil?
Blimey! Never thought I'd see one of those again. If it's the one I'm thinking of it replaced the 706 type as it was cheap. It was so light it moved away from you across the desk when you tried to dial. It was so bad that they were all dumped and replaced ad great expense with the 706.
Were they made by Plessey? Don m5aky |
7th May 2015, 6:42 pm | #7 |
Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Early Telephone with no induction coil?
I suspect that one of mine at least is Ericson as the model number starts N2020.
- Joe |
7th May 2015, 7:29 pm | #8 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,127
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Re: Early Telephone with no induction coil?
Thanks, for that circuit, Joe. Methinks it may be worth me sticking those three resistors and one capacitor* inside a candlestick telephone I have for which I don't have a corresponding bellset - after all, this doesn't really have space for an IC in the base (unless I use a mini one from a 700 series 'phone).
*C1A/B can, of course, be ignored if one is wiring for connection via a UK master socket.
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16th May 2015, 9:54 pm | #9 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Early Telephone with no induction coil?
You are right, it is made, I have some but sets with this diagram, but I hate the bad sound quality. It would be better with only a coil and a capacitor.
dsk |
16th May 2015, 10:06 pm | #10 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
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Re: Early Telephone with no induction coil?
By moving the capacitor in your simple (second) circuit to the other side of the receiver, it is usable with a handset that has a common connection for transmitter and receiver.
How critical is the inductance value of the coil - which I appreciate is to provide a DC path to the transmitter?
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17th May 2015, 4:34 pm | #11 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Early Telephone with no induction coil?
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18th May 2015, 7:08 pm | #12 | |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Early Telephone with no induction coil?
Quote:
The coil is not critical, the idea is to block for voice, and let DC come trough. The resistance should not be as high as it keeps the current under 25 mA. Usually a relay coil do the job. Some even use a resistor, but that may cause higher loss of voice in your own receiver. I have even seen some skip it all, and just puts transmitter and receiver in series, the reason for not doing that are a tendency of weakening the receivers permanent magnet. dsk |
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18th May 2015, 9:18 pm | #13 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
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Re: Early Telephone with no induction coil?
Yes, I've always had drummed into me that it's not good to pass the DC (needed to power the transmitter) through the receiver for that very reason.
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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
30th May 2015, 10:06 am | #14 |
Heptode
Join Date: Jul 2007
Location: Flintshire, UK.
Posts: 707
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Re: Early Telephone with no induction coil?
I have a couple of GPO telephones for use on the public network which don't have an induction coil! A automatic candlestick Tele No 72 with Dial No 1 (made by ATM in 1913 when Epsom & HQ PABX were their only two auto exchanges) - used with a Bellset No 8 (no induction coil) and the wall version of the same Telephone - a Telephone No 55. They use a special version of the Bell Receiver which doesn't have a permanent magnet - it acts as an electro-magnet!
Plessey did produce the horrible cheap 'Plesseyphone' without the induction coil (Telephone Rentals bought much of their kit from Plessey at Beeston) but they also had a telephone which externally looked like a Tele 706 but inside was an induction coil-less circuit designed for use on PAXs. Cheaper to produce than a Tele706 but with other common parts - most were produced by Plessey's 'AEP' factory in Portugal. |