UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Telephony and Telecomms

Notices

Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment

Reply
 
Thread Tools
Old 8th Aug 2017, 4:25 pm   #1
ThePillenwerfer
Heptode
 
ThePillenwerfer's Avatar
 
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 969
Default REN, Resistors &c.

Following on from this thread to save dragging it Off Topic: http://www.vintage-radio.net/forum/s...273#post966273


There's a Wikipedia article here: https://en.wikipedia.org/wiki/Ringer_equivalence_number which says that it is a thing that's used internationally, though with differing definitions.

I know that the GPO/BT maximum of 4 is conservative and, unless you are on a very long line, it'll really be more. When I was young and daft (guess which one of those still applies ) I connected a load of 700s to a BT line and they all rang. Assuming the ones with 500Ω coils and no resistors have a REN of 4 I must have been pulling about twenty.

The problem I've had with trying to work it out is not knowing the inductance, and therefore the Inductive Reactance of bell coils.

The only problem I've had was quite recently. I converted an ATM T3903 to a 232 configuration. I remarked at the time that it's bell coils were 1,000Ω and didn't expect this to matter. With a 2.2kΩ resistor that bell made a pathetic tinkle but was fine without. I then found that for all that that one worked it was pinching all the current so changed those coils for 2,000Ω ones. I did notice that the originals seemed very skinny so am inclined to think that it was their Inductive Reactance, or lack thereof, that was the problem. I also wonder if this is why things like 250s and 704s have two 250Ω coils which are short and fat so, maybe, more inductive than the usual type.

I've never fully understood the need for resistors as if I put several bells in parallel the total Inductive Reactance will increase and reduce the current drawn anyway. If this is the case though I can't see why the GPO would have bothered to change over to 2,000Ω.
Attached Thumbnails
Click image for larger version

Name:	Bell Motor.jpg
Views:	52
Size:	41.0 KB
ID:	147542  
__________________
"Experts are only good at one thing: explaining why something will not work!"
ThePillenwerfer is offline   Reply With Quote
Old 8th Aug 2017, 6:46 pm   #2
TonyDuell
Octode
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 1,932
Default Re: REN, Resistors &c.

Quote:
Originally Posted by ThePillenwerfer View Post
I've never fully understood the need for resistors as if I put several bells in parallel the total Inductive Reactance will increase and reduce the current drawn anyway. If this is the case though I can't see why the GPO would have bothered to change over to 2,000Ω.
Come again? If you put inductors in parallel then unless there is some magnetic coupling between them (which in the case of telephone bells would seem unlikely) they behave like resistors in parallel. The reactance will decrease.
TonyDuell is offline   Reply With Quote
Old 8th Aug 2017, 6:59 pm   #3
ThePillenwerfer
Heptode
 
ThePillenwerfer's Avatar
 
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 969
Default Re: REN, Resistors &c.

AC Theory always gave me nose-bleeds. I was obviously mixing them up with capacitors. Thanks for the clarification.

The point about different shapes possible having different reactions stands though.
__________________
"Experts are only good at one thing: explaining why something will not work!"
ThePillenwerfer is offline   Reply With Quote
Old 8th Aug 2017, 8:01 pm   #4
AndiiT
Octode
 
AndiiT's Avatar
 
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,521
Default Re: REN, Resistors &c.

Hi,
REN has always been a bit of a grey area as far as I'm concerned and I agree that in most cases line length will be a contributing factor to how much, or how little, REN is available on any line.

I recall seeing a comment, in many telephone instruction manuals in the early/mid 1980's after the introduction of the "new" plug and socket system that went something along the lines of "mixing different types of calling devices on an exchange line may result in not all the (your) phones ringing"

I always understood the "different types of calling device" comment to mean tone callers and bells and figured that the reason all the phones may not ring, if an inductive bell and a capacitive tone caller were connected on the same lane, would be due to the ringing current being shorted out by a combination of the inductance and capacitance of the bell motor and tone caller being resonant at a particular frequency which looked like a short circuit to the ringing current.

Regards

Andrew
AndiiT is offline   Reply With Quote
Old 8th Aug 2017, 8:06 pm   #5
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Quote:
Originally Posted by ThePillenwerfer View Post

The problem I've had with trying to work it out is not knowing the inductance, and therefore the Inductive Reactance of bell coils.
I got my figure for a type 59A bell movement by driving it with a 25Hz 90V supply via a resistor and a true RMS ammeter, and measuring the voltage across the bell-movement (and hence its impedance), the supply, and the resistor.

From this I could draw a triangle with each side representing the aforementioned voltages, and using the Cosine rule, extrapolated the in-phase and quadrature components for the bell-movement: typically 1776 + j2085, or a Z of 2739 at an angle of +50 degrees.

This differs from that of a bridged measurement because of the current and the 'in-phase' losses (eddy current and hysteresis losses) and gives an inductance of about 13H.
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 8th Aug 2017, 9:19 pm   #6
Oldcodger
Heptode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 896
Default Re: REN, Resistors &c.

Simple solution to the low bell situation is to fit a BT socket as used on systems . Don't know the type/part no, and don't have one to hand, but it had circuitry inside, which when Driven by a 50v from the system gave extension bells some oomph. Then again, there's the ringer converters as fitted to system phone systems( where there was no provision for an extension bell ) to have an outside bell ring on external calls.
Oldcodger is online now   Reply With Quote
Old 8th Aug 2017, 9:45 pm   #7
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Quote:
Originally Posted by AndiiT View Post
if an inductive bell and a capacitive tone caller were connected on the same lane, would be due to the ringing current being shorted out by a combination of the inductance and capacitance of the bell motor and tone caller being resonant at a particular frequency which looked like a short circuit to the ringing current.
But would they not be in parallel, and so draw minimum current from the line ringing supply at resonance?
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 8th Aug 2017, 9:52 pm   #8
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Quote:
Originally Posted by Oldcodger View Post
Simple solution to the low bell situation is to fit a BT socket as used on systems . Don't know the type/part no...
A REN extender? I have a BT one of those: RS used to sell them years ago. They take a 75V 25Hz signal and regenerate it, rather than supply a 25Hz ringing current from d.c. but yes...

An external mains supply is needed, of course.

http://uk.rs-online.com/web/p/teleph...ories/2079519/
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 8th Aug 2017, 11:06 pm   #9
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Evidently the European Telecommunication Standard REN is defined (REN 1) as a simulated ringer detector circuit consisting of a 55 H inductor in sries with a 7 kilohm resistor, and is based on the characteristics of the dynamic impedance of a type 59D bell movement.

From my extrapolation method described earlier I reckon the 59D (the one with the 4000 Ohm @ d.c. bell-movement) is 7186 + j8275, or a Z of 10960 Ohms at 25Hz, which near as dammit fits the spec.
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 9th Aug 2017, 4:16 pm   #10
els1967
Tetrode
 
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 72
Default Re: REN, Resistors &c.

I wanted to put a 312 and a modern phone/answerphone on the same extn but when I tried this with the unconverted 312 the answerphone wouldn't answer the call until I "converted" the 312. I presume the 312 was hogging so much current the modern phone couldn't detect the ring. Or something.
els1967 is offline   Reply With Quote
Old 9th Aug 2017, 5:55 pm   #11
radiotechnician
Pentode
 
Join Date: Jan 2013
Location: Powell River, British Columbia, Canada.
Posts: 161
Default Re: REN, Resistors &c.

The insets below may shed some light ono issues of ringer loads, dating
back to the step-by-step days,

As an aside, the wire chief desk test gear included a very sensitive
galvanometer. In days where additional (unpaid) phones were hunted down,
the kick-up of that instrument could detect if extra ringers lurked on a line.

Needless to say, being raised in a telco family, sometimes served well
in days of youth.
Attached Thumbnails
Click image for larger version

Name:	Ringing Sect 1.jpg
Views:	64
Size:	93.6 KB
ID:	147599   Click image for larger version

Name:	Ringing 2.jpg
Views:	57
Size:	93.9 KB
ID:	147600  
__________________
Steve Dow
VE7ASO
radiotechnician is offline   Reply With Quote
Old 9th Aug 2017, 6:43 pm   #12
Dave Moll
Dekatron
 
Dave Moll's Avatar
 
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 3,155
Default Re: REN, Resistors &c.

The above presumably relates to ringers in series, given that this was the norm in the days before plug-in 'phones, where the greater proportion of the ringing voltage would be across a high-impedance ringer. A slightly different situation arises with the present arrangement of parallel ringers where the greater proportion of the available current will pass through the low-impedance ringer, which is significant if the load causes the total voltage to drop. The situation encountered by els1967 may be that the 312 was more tolerant of a reduced voltage than was the answerphone.
__________________
Mending is better than Ending (cf Brave New World by Aldous Huxley)
Dave Moll is offline   Reply With Quote
Old 9th Aug 2017, 8:16 pm   #13
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 6,157
Default Re: REN, Resistors &c.

If the answering machine has a ringing detector which relies on a reverse-biased Zener diode going conductive, then it's conceivable that a high-REN phone in parallel with it could pull the voltage down just too low for the Zener diode to start conducting. It probably will impose some additional loading of its own, just to guard against false positives from noise on the line.
__________________
Julie {formerly known AJS_Derby}
julie_m is offline   Reply With Quote
Old 9th Aug 2017, 8:51 pm   #14
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Quote:
Originally Posted by julie_m View Post
conceivable that a high-REN phone in parallel with it could pull the voltage down just too low for the Zener diode to start conducting. .
The voltage dropped across an unmodified 312 bell (or any 59A bell movement phone) is greater than the voltage dropped across a modified (bell plus 3k3 resistor) telephone: for a 75V 25Hz supply, say, 89V and 78V respectively. But this is without the extra loading of the high-REN answerphone, which I wouldn't have thought to be that severe a load anyway.

I was going to suggest the ringing voltage might be too high, but the spec says 100V down to 40V, so any BABT equipment should be OK.
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 18th Sep 2017, 9:20 pm   #15
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

I would always use a 3k3 resistor on a Trimphone. I plugged in my (un-resistored) 1975 722 Mk:2 and the bell on my N1071 (Type 59A bell with 3K3 resistor in series) fell silent when it was meant to ring.

So I did a few tests... When I put the Trimphone on my ringing generator supply (nominal 100V unloaded) it drew nearly 59mA and pulled the voltage down to 47.3V! This gives it an impedance (the Trimphone ringer is near as dammit resistive) of 800 Ohms(ish): a very high REN! Not a problem with series bells on the old system.

To complicate matters, the impedance follows an inverse curve and varies from 1962 Ohms driven with 5mA to 800 Ohms driven with 59mA.

The unmodified Trimphone was shunting the 59A bell and 3k3 resistor combo and sinking the combined ringer impedance to about 710 Ohms: only the Trimphone sounded, and most of the ringing voltage was being dropped across the 1u8 cap in the master LJU.

With a 3k3 resistor in the Trimphone and an unmodified 59A bell movement, the combined impedance will be around 1800 Ohms Z. With a 3k3 resistor in the Trimphone and an 3k3 resistor 59A bell movement, the combined impedance will be around 2390 Ohms Z. Both Trimphone and Type 59A bell movement instrument will ring.

The good news is that the Trimphone volume is hardly affected. The sounder is cleverly designed to point downwards and utilise the gap between the base of the telephone and the surface upon which the telephone is mounted to resonate the audio tone produced. (I've exploited this on Morse oscillators in the past by mounting a flat plate a centimetre or co above the hole behind which a rocking-armature 4T inset receiver is mounted).

The current drawn by the Trimphone is unaffected by the volume / off control.
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 18th Sep 2017, 10:15 pm   #16
ThePillenwerfer
Heptode
 
ThePillenwerfer's Avatar
 
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 969
Default Re: REN, Resistors &c.

I found the same thing recently, Russell. I upped R9 on the Tone Ringer 8A to 4.7kΩ and all was well.

Doesn't setting the volume to 'Off' short the whole thing thereby rendering all bells mute?
__________________
"Experts are only good at one thing: explaining why something will not work!"
ThePillenwerfer is offline   Reply With Quote
Old 18th Sep 2017, 10:55 pm   #17
russell_w_b
Nonode
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 2,591
Default Re: REN, Resistors &c.

Quote:
Originally Posted by ThePillenwerfer View Post

Doesn't setting the volume to 'Off' short the whole thing thereby rendering all bells mute?
The ringer still draws the same current and has the same voltage dropped across the 'bell' wires (T4 and T16) irrespective of whether the switch is off or loud, so I'm presuming it makes no difference (well, OK... There's a couple of milliamperes difference, but that's all. ).

Looking at the graph I plotted re: current versus voltage and thinking about it, I suspect the design brief was for a 1000 Ohm 'ringer' which would draw 20.4mA with the series capacitor on a 75V ringing supply at the premises.
__________________
Regds,

Russell W. B.
G4YLI.
russell_w_b is online now   Reply With Quote
Old 18th Sep 2017, 10:58 pm   #18
Oldcodger
Heptode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 896
Default Re: REN, Resistors &c.

Quote:
Originally Posted by russell_w_b View Post
Quote:
Originally Posted by Oldcodger View Post
Simple solution to the low bell situation is to fit a BT socket as used on systems . Don't know the type/part no...
A REN extender? I have a BT one of those: RS used to sell them years ago. They take a 75V 25Hz signal and regenerate it, rather than supply a 25Hz ringing current from d.c. but yes...

An external mains supply is needed, of course.

http://uk.rs-online.com/web/p/teleph...ories/2079519/
Just noticed the reply. Not an extender( convertor ringing xx )as such- but a normal looking large size socket, with ringing circuitry inside , powered by 50 v DC from a BT system .
Oldcodger is online now   Reply With Quote
Old 19th Sep 2017, 4:15 am   #19
TonyDuell
Octode
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 1,932
Default Re: REN, Resistors &c.

I drew out the circuit of one of those REN boosters some time ago. If anyone wants a copy of it, get in touch. It's quite simple, using a quad darlington optoisolator, a small relay, a 45-0-45V mains transformer and a handful of small components.

Normally all wires of the output side are connected to the corresponding pins of the input BT Plug 431A, so that anti-tinkle works correctly. When it detects a ring signal, the relay operates, disconnecting the output side bell shunt wire from the input side and connecting it instead to a couple of sections of the optoisolator. These are driven by the incoming bell signal and switch the output bell signal between +65V and -65V at the incoming ringing frequency (+/-65V obtained by rectifying the output of the transformer, of course).
TonyDuell is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 10:21 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.