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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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2nd Apr 2015, 10:50 am | #1 |
Retired Dormant Member
Join Date: Apr 2015
Location: Wallasey, Merseyside, UK.
Posts: 1
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Components for GPO 746 Conversions
Hi! All you knowledgeable people out there I am new to the forum so please excuse any mistakes made. My question is when converting a GPO 746 telephone to Plug & Socket working I need your help. The diagrams show use of a 3.3 Kohm resistor, a rectifier element 205, or use of two 1N4001 diodes. I assume that the voltages are 50 volt. I have tried several local electronic outlets without success, so please where do I get them from? Am I actually asking for the right components?
Many Thanks in advance for your assistance. Ace |
2nd Apr 2015, 1:33 pm | #2 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,687
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Re: Components for GPO 746 Conversions
Hello Ace, and welcome.
You don't actually need either diodes or resistor to get the telephone to work. If you're just using the one telephone then leave a link in between terminals 4 and 5. It will work fine. The resistor decreases the REN but drops approximately half your ringing voltage across it. The diodes are to clip off acoustic shock from line-clicks, more pronounced on the sensitive rocking-armature receivers of the 700 series instruments. There're only a few millivolts on the receiver across which the diodes are connected back-to-back, so 50V PIV rated diodes will be way more than adequate. Any old diodes will do that you could scavenge. eBay? Hardly worth bothering the likes of RS or CPC for just a couple. You could always do up the telephone without the aforementioned components and fit them later, when you acquire the bits. The 'proper' rectifier pack (Rectifier, 205) sometimes crop up on eBay too. It's just a couple of diodes encapsulated and fitted with spades.
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2nd Apr 2015, 2:38 pm | #3 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Components for GPO 746 Conversions
Even Zener diodes will do, if you're desperate! The business-end-to-tail-end wiring means that there will never be more than 0.7 V across the pair.
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