Early Telephone with no induction coil? - UK Vintage Radio Repair and Restoration Discussion Forum

Obmcclintock · 27th Mar 2015, 3:19 am

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

dagskarlsen · 27th Mar 2015, 7:17 am

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

Ryan_1993 · 27th Apr 2015, 8:30 pm

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.

AC/HL · 27th Apr 2015, 9:12 pm

The induction coil is inside the bellset, which was a separate unit, presumably missing on yours.

ThePillenwerfer · 7th May 2015, 5:49 pm

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

vosperd · 7th May 2015, 6:29 pm

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

ThePillenwerfer · 7th May 2015, 6:42 pm

I suspect that one of mine at least is Ericson as the model number starts N2020.

- Joe

Dave Moll · 7th May 2015, 7:29 pm

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.

dagskarlsen · 16th May 2015, 9:54 pm

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

Dave Moll · 16th May 2015, 10:06 pm

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?

OscarFoxtrot · 17th May 2015, 4:34 pm

Quote:

Originally Posted by ThePillenwerfer

I've got a horrible Telephone Rentals thing which is designed without one.

Probably intended for use on a PBX with shorter lines, and with less exacting transmission standards than the GPO demanded.

dagskarlsen · 18th May 2015, 7:08 pm

Quote:

Originally Posted by Dave Moll

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?

Yes you may put the capacitor on the other side, the only idea of this is to block DC from receiver. 1 microfarad seems to be a minimum, depends on what you have and the room available.

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

Dave Moll · 18th May 2015, 9:18 pm

Quote:

Originally Posted by dagskarlsen

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.

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.

Pellseinydd · 30th May 2015, 10:06 am

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.

27th Mar 2015, 3:19 am	#1
Obmcclintock Retired Dormant Member Join Date: Feb 2015 Location: Minnesota, USA. Posts: 16	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

27th Mar 2015, 7:17 am	#2
dagskarlsen Heptode Join Date: Jan 2008 Location: Hakadal, Norway Posts: 642	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
Ryan_1993 Hexode Join Date: Sep 2012 Location: Yorkshire, UK. Posts: 329	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.

27th Apr 2015, 9:12 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Early Telephone with no induction coil? The induction coil is inside the bellset, which was a separate unit, presumably missing on yours.

7th May 2015, 5:49 pm	#5
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	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 Attached Thumbnails __________________ "Experts are only good at one thing: explaining why something will not work!"

7th May 2015, 6:29 pm	#6
vosperd Hexode Join Date: Oct 2007 Location: Bristol, UK. Posts: 444	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
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: Early Telephone with no induction coil? I suspect that one of mine at least is Ericson as the model number starts N2020. - Joe __________________ "Experts are only good at one thing: explaining why something will not work!"

7th May 2015, 7:29 pm	#8
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	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. __________________ Mending is better than Ending (cf Brave New World* by Aldous Huxley)

16th May 2015, 9:54 pm	#9
dagskarlsen Heptode Join Date: Jan 2008 Location: Hakadal, Norway Posts: 642	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 Attached Thumbnails

16th May 2015, 10:06 pm	#10
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	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? __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

30th May 2015, 10:06 am	#14
Pellseinydd Heptode Join Date: Jul 2007 Location: Flintshire, UK. Posts: 707	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.