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 3rd Feb 2017, 12:45 am   #1
boombox
Pentode
 
Join Date: Mar 2012
Location: Rotherham, South Yorkshire, UK.
Posts: 152
Default How involved is connecting two extensions to a Bellset 20?

It seems I may be about to buy a Bellset 20 - just curious how difficult someone with no telecoms experience would find wiring it up to work with two converted 746 telephones and a main BT line?

I can solder, I can crimp plugs, I can use a multimeter...but that's about it. I certainly can't read circuit diagrams yet.

Thanks!
boombox is offline  
Old 3rd Feb 2017, 9:08 am   #2
Dave Moll
Dekatron
 
Dave Moll's Avatar
 
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Re: How involved is connecting two extensions to a Bellset 20?

No soldering or crimping needed - unless you wish to add spade terminals to ends of wires. All connections in the BS 20 are (like most telephone equipment) screw terminals, nor do you need to decipher any circuit diagrams.

From memory (without actually digging out my own unit), connecting converted 746s would be a matter of connecting a pair or master sockets to the terminals in the BS 20 with the appropriate labels. Unconverted ones could be connected direct. The only minor complication is wiring in the magneto for ringing the main station from the extension - it has three terminals: one common to line and 'phone, one to line and one to 'phone - and operates such that the 'phone is normally connected direct to the line, but that when the handle is turned it operates a switch that disconnects the extension 'phone and connects itself accross the line to send its ringing current. N.B. all references here to "line" refer to the connection running from the extension to the main unit.
__________________
Mending is better than Ending (cf Brave New World by Aldous Huxley)
Dave Moll is online now  
Old 3rd Feb 2017, 11:09 am   #3
els1967
Pentode
 
Join Date: Aug 2016
Location: Dunstable, Bedfordshire, UK.
Posts: 139
Default Re: How involved is connecting two extensions to a Bellset 20?

How would it be possible to connect it to the BT line? I'm not an expert but won't the bellset need some sort of conversion to get the bells to work? I've always used a PABX so never had this kind of issue before.
els1967 is offline  
Old 3rd Feb 2017, 11:32 am   #4
Dave Moll
Dekatron
 
Dave Moll's Avatar
 
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Re: How involved is connecting two extensions to a Bellset 20?

Very simple. There is another pair of terminals for the A and B connections (usually white and red respectively) of a standard BT line cord. From memory, the bells will operate via an internal capacitor (condenser). I don't recall whether it is possible to wire it for three-wire working.

I really must dig out my Bellset 20 and check whether my various recollections are correct.
__________________
Mending is better than Ending (cf Brave New World by Aldous Huxley)
Dave Moll is online now  
Old 3rd Feb 2017, 6:37 pm   #5
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
Default Re: How involved is connecting two extensions to a Bellset 20?

I know the OP said he doesn't read circuit diagrams, but for reference the diagrams for this are N520 (Bellset 20) and N4309 (Plan 7). 'Plan 7' was the GPO jargon for a main telephome on the bellset with one extension. The diagrams are available from Sam Hallas's site (search on google for N diagram)

It is very easy, I think. The main telephone should be wired as it was originally (i.e. not convereted to the modern plug). All 3 wires (A, B, Extension Bell) of that telephone are connected to their own terminals on the bellset.

The extension telephone is also wired as it was originally, but now the extension bell wire is strapped to the A wire externally. This gives a 2-wire telephone. I think it's all pretty clear in the diagram, but I am used to reading them.

For signalling (ringing) from main to the extension there is a magneto generator (wind the handle) in the bell set. For signalling from the extension to the main you can either fit a DC bell at the 'main' end and a button at the extension (the extra circuit is essentially that of a doorbell), which is known as an 'internal extension) or fit a magneto (known as a Generator No 26 AP) at the extension which will then ring the normal bell at the main telephone (this is called an 'external extension' in the diagram).
TonyDuell is offline  
Old 3rd Feb 2017, 9:16 pm   #6
Oldcodger
Nonode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
Default Re: How involved is connecting two extensions to a Bellset 20?

Not trying to be pedantic .
One point to be aware of-the use of more than one capacitor in a circuit has always been discouraged due to the possibility of ring trip( where bells ring only once or not at all and caller says that call has been answered). With the OP having problems with circuit diagrams, best place to wire in bell is ( without capacitor) between terminals 3 & 5 of master socket ( or any other three wired extension socket).
Oldcodger is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:28 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.