UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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

Closed Thread
 
Thread Tools
Old 17th Jan 2012, 9:54 pm   #1
Twin Pin
Retired Dormant Member
 
Join Date: Jan 2012
Location: Ayrshire, Scotland, UK.
Posts: 5
Default Belgian Bell Telephone conversion issues

A few years ago I purchased a Belgian "Bell Telephone". It is not marked with a model number but I have seen this particular style being referred to as the "Bell Gurder" - the body is made of painted copper and mounted on a large, square base with grilles around the bells (see attached picture).

This telephone came to me with no line cord or handset cord attached, also the receiver and microphone inserts were missing. I re-fitted the handset with a new microphone and receiver and attempted to wire it to the telephone. Problems then arose in that the eight contacts inside the telephone are unmarked whilst the wiring diagram, (attached picture), does not give an indication of the physical location of the contacts. After much painstaking tracing I managed to identify which contact was which and have labeled the in pencil (please see attached picture).

I attempted to connect a BT line cord and have succeeded to a point - the receiver and microphone work and the bells ring, but the dial does not function. When turning the dial, the receiver is cut off, but when returning no pulses are sent on the line and the dial tone continues. My line supports pulse dialling - I only use dial telephones on it - and the line cord and socket are functioning correctly. I have converted other telephones but have always had instructions, so this one currently has me a little stumped!

Does anyone have any experience of converting this particular model of telephone? Any hints and tips would be gratefully received.

I should mention - the outermost contacts on both the left and right hand side are not connected to anything within the telephone. Also - the dial and switch hook contacts have been checked, cleaned and are working correctly.
Attached Thumbnails
Click image for larger version

Name:	Phone.JPG
Views:	297
Size:	90.1 KB
ID:	61325   Click image for larger version

Name:	Terminals.JPG
Views:	298
Size:	134.5 KB
ID:	61326   Click image for larger version

Name:	Diagram.JPG
Views:	310
Size:	108.1 KB
ID:	61327  
Twin Pin is offline  
Old 17th Jan 2012, 11:14 pm   #2
AndiiT
Octode
 
AndiiT's Avatar
 
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,784
Default Re: Belgian Bell Telephone conversion issues

Hi,
Only a guess but try replacing strap A-S with a 3k3 resistor. Looking the circuit of your telephone it's possible that the 1k bell is damping the dial pulses across the line - to prove this you could just remove the strap and see if the dial then pulses out to the line.

You will always have to have this phone wired as a "two-wire" device (i.e. no Blue lead connected from the line cord) due to the way that the bell is wired in circuit. Red of line cord to the B terminal and White to the A terminal (I am sure that you already knew this)

I have just looked at your pictures and see that the line cord isn't connected as mentioned above, this may be the cause of your lack of dial pulses as it appears that the Red of the line cord is connected after the point that the dial would break the line, you need to connect for two wire working as mentioned above; The only downfall wiring this way is that you will suffer bell tinkle on any extensions when dialling out.

Regards
Andrew
AndiiT is offline  
Old 18th Jan 2012, 12:13 am   #3
Twin Pin
Retired Dormant Member
 
Join Date: Jan 2012
Location: Ayrshire, Scotland, UK.
Posts: 5
Default Re: Belgian Bell Telephone conversion issues

Thanks for the recommendation of the two-wire approach - the set-up shown was based upon a bit of trial and error and did work (with the exception of the dial), but obviously wasn't the right way to do it.

Just gave it a try (Red >B, White >A and 3.3K resistor between A and S). Receiver, microphone and switch hook still working fine. Bell ring is working but very "one-sided" if you catch my drift; before it was ringing both bells but now it seems to be tending toward one side more than the other, and is quite weak. Dial is still not functioning.

Could the problem lie in the wiring of the handset? In the contact picture, to the left, the handset wires are shown. Blue is microphone, red is mic+receiver and green is receiver. I am also using a modern microphone as opposed to a carbon granule job, which could be affecting things. I have tried bridging the microphone and testing the dial but the situation remains the same. As I mentioned before, the original receiver and transmitter were missing, so a 4T receiver and 21a transmitter have been fitted instead.

I am not ruling out that I may have made a mistake in my tracing of the contacts - it really is a nest of wiring in there! Presumably the Belgian engineers had a diagram of the contact locations.
Twin Pin is offline  
Old 18th Jan 2012, 9:55 am   #4
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
Default Re: Belgian Bell Telephone conversion issues

I see there's a note on the diagram stating that for T an U installations (I assume that means a manual exchange) a strap should be inserted between terminals b and M. This strap shorts out the dial pulsing contacts, so if it's fitted in your phone the dial won't work.

You could try connecting a meter set to ohms range, preferably an analogue one, between b and M. Rotate the dial and as it returns you should see the needle oscillate if the dial is working and not shorted.
__________________
Graham. Forum Moderator

Reach for your meter before you reach for your soldering iron.
Station X is offline  
Old 18th Jan 2012, 10:46 am   #5
AndiiT
Octode
 
AndiiT's Avatar
 
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,784
Default Re: Belgian Bell Telephone conversion issues

Hi,
I have just noticed that the bell capacitor is only 1uF, this may be contributing to the weak ringing as the standard value in the UK is 1.8uF (originally 2uF) you could try substituting the 3k3 resistor across terminals a-s for a 1uF non polarised capacitor to see if that improves ringing.

Wired with the Red of the line cord to the B terminal and the White of the line cord to the A terminal, with no other colours of the line cord connected, I can't see any reason why the phone shouldn't pulse out although there is a 40 Ohm resistor to consider but that shouldn't make a lot of difference.

It might be worth trying to ensure that you have correctly identified the terminals, also check that the contacts which short out the transmitter and receiver during dialling are operating correctly as if they are high resistance or open circuit the dial pulses then have to travel through the added resistance of the handset circuity.

Regards
Andrew
AndiiT is offline  
Old 18th Jan 2012, 3:57 pm   #6
tele919er
Retired Dormant Member
 
Join Date: Mar 2011
Location: London, UK.
Posts: 7
Default Re: Belgian Bell Telephone conversion issues

Would have thought the easiest way to check this is to connect a meter, set to low scale resistance, across a and b and slowly return the dial to normal. If all the contacts are good (are the off-normals connecting OK) and it's wired as per the diagram you should get pulses of open circuit - 37ohm loop - opencircuit.

On a GPO telephone the dial pulses are a pure short circuit loop. This telephone (as wired) includes 37 ohms although I don't think this is that significant although it can't help for good dial pulses.

Have you checked the 0.1uF capacitor is not short circuit?

Last edited by tele919er; 18th Jan 2012 at 4:05 pm.
tele919er is offline  
Old 18th Jan 2012, 11:45 pm   #7
Twin Pin
Retired Dormant Member
 
Join Date: Jan 2012
Location: Ayrshire, Scotland, UK.
Posts: 5
Default Re: Belgian Bell Telephone conversion issues

What a long evening this has been! I started by double-checking my terminal post identifications and confirmed that they were correct. I then tested the continuity of the dial contacts and they were ok. Then I tried tele919r's suggestion and checked the resistance between A and B when dialling. I was surprised to find that it was switching between 37 Ohms and 77 Ohms, not 37 Ohms and open circuit as it should have been. Attention was then drawn to the 1uF capacitor - if it was short-circuit then it would add the 37 Ohm and 40 Ohm coils between A and B to give the 77 Ohm resistance I was getting.

Sure enough it was! I found a 1.8uF GPO (ex-700 series) capacitor in my spares box, fitted it in place of the faulty one, and the telephone now works! I also checked the 0.1uF capacitor and it is giving near enough the correct value on the capacitance meter.

Many thanks for all the help, I really was quite lost before and would have still have been struggling with three wires and guesswork if it wasn't for all your suggestions.
Twin Pin is offline  
Old 19th Jan 2012, 10:25 pm   #8
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Belgian Bell Telephone conversion issues

Quote:
Originally Posted by Twin Pin View Post
Just gave it a try (Red >B, White >A and 3.3K resistor between A and S). Receiver, microphone and switch hook still working fine. Bell ring is working but very "one-sided" if you catch my drift; before it was ringing both bells but now it seems to be tending toward one side more than the other, and is quite weak.
Shame on us for not picking up on this sooner. That is suggestive of DC getting through to the bell, meaning the capacitor is either leaky or shunted.

Oh, well, I suppose everything's obvious once you know it .....
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline  
Old 1st Nov 2016, 7:27 pm   #9
Tiggermoth
Triode
 
Join Date: Nov 2016
Location: Manchester, UK.
Posts: 19
Default Re: Belgian Bell Telephone conversion issues

I was so delighted to find this topic!

I bought an unconverted old telephone from a second hand shop last week and didn't have a clue what it was until I saw the photos on this thread.

With this help I've got it going as a two-wire telephone. I've added back-to-back diodes across the receiver terminals in the phone because of a massive 'click' when going on & off hook. I've also added the innards of a Transmitter 21A for the microphone because the original carbon one was dreadful!

At first callers got an echo. I reversed the 21a terminals and the problem went away (not sure why) or possibly I'd managed to just improve the mic position or something.

Attached is the circuit diagram in mine. The terminal numbers are painted on the inside of the case (I'll post that tomorrow).

T
Attached Thumbnails
Click image for larger version

Name:	IMG_20161028_195701.jpg
Views:	132
Size:	88.5 KB
ID:	132111  
Tiggermoth is offline  
Old 2nd Nov 2016, 9:52 pm   #10
Tiggermoth
Triode
 
Join Date: Nov 2016
Location: Manchester, UK.
Posts: 19
Default Re: Belgian Bell Telephone conversion issues

I found this page too (if you go to the bit called Bell Manufacturing Co. Diagram ST132 ) it gives the conversion method.

http://www.britishtelephones.com/pstconv1.htm#non

It seems a bit different to the ideas given above - I'm not sure what is achieved by the suggestion to disconnect the wire from the 1uF capacitor and connect to the blue line cord?

Any ideas please?

I've still not managed to take a photo of the innards of the telephone yet, but here it is (with a new braided handset cord)

T
Attached Thumbnails
Click image for larger version

Name:	my_belgian_phone.jpg
Views:	117
Size:	79.2 KB
ID:	132167  
Tiggermoth is offline  
Old 3rd Nov 2016, 7:55 am   #11
Dave Moll
Dekatron
 
Dave Moll's Avatar
 
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Re: Belgian Bell Telephone conversion issues

Quote:
Originally Posted by Tiggermoth View Post
I'm not sure what is achieved by the suggestion to disconnect the wire from the 1uF capacitor and connect to the blue line cord?
This is to use the ringing capacitor in the UK master socket rather than the one in the bellset itself, the purpose of which is to prevent bell-tinkle on other 'phones by ensuring that all bells are in parallel and short-circuited by the dial-off-normal contacts during dialling. If this is not considered a problem - or there are no other 'phones on the line with mechanical bells - it can be ignored.
__________________
Mending is better than Ending (cf Brave New World by Aldous Huxley)
Dave Moll is online now  
Old 3rd Nov 2016, 3:27 pm   #12
peter_sol
Octode
 
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
Default Re: Belgian Bell Telephone conversion issues

You will need to put a 3.3K resistor in series with the bell coil
peter_sol is offline  
Old 16th Nov 2016, 11:24 am   #13
Tiggermoth
Triode
 
Join Date: Nov 2016
Location: Manchester, UK.
Posts: 19
Default Re: Belgian Bell Telephone conversion issues

Dave & Peter,

Thank you both for your replies. They make sense. I hadn't thought of the separate wiring of the bell wire, but it makes sense now - and the 3.3K resistor too.

Right, I've finally got round to opening the telephone up again to show the labelling of the terminals that was painted on the inside of the telephone.

Hopefully, it will help somebody else with the same telephone. It might even help me when I forget all about it and find another phone the same.

So, looking at the telephone upturned with the base off it, and the wires pointing away from me, they are labelled as

[Blank], E, L1, L2 R, RT, T, [Blank]

(In the photograph I've managed to miss off the blank terminal on the right)

As you can see on the photograph, it's currently wired up as a two-wire telephone. I have a 3.3k resistor from L1 to E to reduce the bell current to bring it to REN 1. The back-to-back diode pair is shown in the red sleeve between R and RT.

Oh, and as you might spot, my brown braided handset cable is actually three core braided mains cable!

I've also photographed the bottom of the phone, which is painted with 2712-A-RB or it could be 2712-A-R13.

T
Attached Thumbnails
Click image for larger version

Name:	inside_of_bell_telephone_showing_terminal_labels.jpg
Views:	106
Size:	103.1 KB
ID:	132876   Click image for larger version

Name:	2712-A-RB.jpg
Views:	97
Size:	72.6 KB
ID:	132877  
Tiggermoth is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:12 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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.