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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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23rd Jul 2007, 11:37 am | #1 |
Retired Dormant Member
Join Date: Jul 2007
Location: london
Posts: 1
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BT/GPO 746 Dial Problem
Hello folks,
I have a proplem with an old 746 phone. The dial was very sticky and slow on returning once dialed. I decided to unscrew the dial to se if there was anything obvious I could do. Unfortunately, once I had taken the clear plastic dial off, I unscrewed the 2 smaller screws underneath the dial and heard an ominous 'ping'. Now the dial hardly works and has no tension. Could anyone point me to a site that has information and diagrams for repairing this problem. Or does anyone have any other tips? Many thanks, Sam |
24th Jul 2007, 12:42 pm | #2 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,864
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Re: BT/GPO 746 Dial Problem
Hi Sam and welcome!
The simplest solution would be to look for a new dial mechanism, especially as yours sounds like it was past its best anyway. They often turn up on eBay for less than a fiver, and are frequently NOS or New Old Stock, i.e. are still in their unopened original GPO packing Nick. |
24th Jul 2007, 2:46 pm | #3 |
Octode
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,786
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Re: BT/GPO 746 Dial Problem
Hi,
You might find some information here http://www.britishtelephones.com/ Nicks suggestion of a replacement dial seems like a good one though, I too have never had much luck with slow/broken dials. Andrew |
24th Jul 2007, 4:45 pm | #4 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
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Re: BT/GPO 746 Dial Problem
At the risk of inducing apoplexy in all the ex-GPO types here, I wish to add the following: not much use with a 746 dial admittedly, but I have had great success with the more substantial metal dial of the type 300 instrument.
These older dials can be stripped of their plastic parts and boiled in water for about 20 minutes to remove all grime and filth, then re-lubricated immediately with light clock oil - even WD40. All I can suggest for the 746 type of dial is to apply judiciously some PTFE lubricant spray to the moving parts. Don't be tempted to clean it with 'Inhibisol' or 'Colclene' degreasers, unless you are sure that they are the sort of chemical that doesn't dissolve plastic. Just thought I'd mention it... -- Regds, Russell W. B. |
25th Jul 2007, 8:45 am | #5 |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: BT/GPO 746 Dial Problem
Hmmm - WD40 is not really a lubricant. Clock oil should be fine as it stays where it is. I did dismantle and lubricate a similar mechanism on my Avo CT160 valve tester.
Sam Your "ping" was probably the spring that is pre-tensioned. Others will know more about this than I; someone will sort you out!
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Mike. |
25th Jul 2007, 10:33 am | #6 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
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Re: BT/GPO 746 Dial Problem
When you took the plastic dial off, presumably you unscrewed the two small screws in the centre boss, either side of the dial mounting screw. As Mike points out, these screws retain the coiled-up tensioning spring (rather like a clock mainspring) held in the brass cup below the pulsing disc on the back. You could try:
To gain access to the governor and operating mechanism, all that is necessary is to remove the small spring-clip on the number disc behind the dial, which simply lifts off. Apply appropriate lubrication here. The governor should not normally need adjusting (I have found) and is held at one end in an adjustable brass cup, accessible behind the dial on the edge of the casing. Don't release both nuts on the thread, as you'll lose the position of the pulsing disc in relation to the finger plate! HTH
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Regds, Russell W. B. G4YLI. |
3rd Feb 2008, 11:44 am | #7 |
Retired Dormant Member
Join Date: Feb 2008
Location: Maidstone
Posts: 9
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Re: BT/GPO 746 Dial Problem
Please please please never use WD40 to lubricate a dial. It will work for a short time but will collect dust and clog it up even worse than before. I can do dial repairs be they slipping cam types ( No10 ) or trigger types (No12 or 21 )
PM me if anyone requires help Cheers Andy |