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Old 20th Oct 2007, 10:26 pm   #1
Darren-UK
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Default Tele 312 terminal block.

I've been converting a 312 for PST use and have a head-scratcher with the terminal block and its strapping.

It's been so long since I've converted a 300 series telephone that I had to look up the procedure on Bob Freshwater's site. Here we are told, as part of the procedure to destrap T10-T11 and T12-T13, then strap T1-T2-T3-T9. Presumably this means strap T1-T2 and T3-T9. The actual instructions are on this page.

However, it is impossible to strap T3 to T9 due to the terminal positions. They are in three rows on the block, numbered left to right, right to left, left to right accordingly.

Can anyone put me right on this please ? Has Bob made an error ? I did email him a few days ago but no reply has been forthcoming.

Curiously, I have another 312 on PST and this still has T10-T11 and T12-T13 strapped. The resistor (for the REN) is across T1-T2 whereas Bob's site says it should across T11-T12. This telephone works perfectly ok with this wiring configuration .
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Old 21st Oct 2007, 1:46 am   #2
Tim
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Default Re: Tele 312 terminal block.

Quote:
Presumably this means strap T1-T2 and T3-T9.
As it says, T1-T2-T3-T9. Connect a wire to T1 then to T2 then to T3 then to T9
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Old 21st Oct 2007, 5:33 pm   #3
Dave Moll
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Default Re: Tele 312 terminal block.

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Originally Posted by darren-uk View Post
Curiously, I have another 312 on PST and this still has T10-T11 and T12-T13 strapped.
Looking at the circuit diagram, it would appear that you are using the internal ringing capacitor rather than the one in your master socket. Although this works, it is not the recommended approach.

Quote:
The resistor (for the REN) is across T1-T2 whereas Bob's site says it should across T11-T12.
Again, looking at the diagram, this resistor seems to be across the diodes etc. at the "bottom" end of the bell. I'm not convinced that it is actually doing anything useful there*. The suggested strapping shorts out this network (which is not needed) and inserts the resistor between the bell and the blue wire from the master socket (ringing capacitor), disconnecting the connection to the internal capacitor.

Where, if at all, is the blue wire of the line cord connected on this 'phone?

*edit: on second thoughts, if that switch between T1 and T9 is open, the resistor is doing the same as it would be at the "top" end of the bell.
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Old 21st Oct 2007, 9:25 pm   #4
AndiiT
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Default Re: Tele 312 terminal block.

Hi,
Strapping on any telephone instrument does not necessarily refer to straps adjacent to one another.
If you needed to strap terminals that where a few numbers apart it was/is quite in order to use a short piece of "jumper" wire of the type commonly used in the street cabinets and at the exchange Main Distribution Frame, of course if you do not have access to this type of wire a plain old bit of insulated single strand stiff wire will suffice.

In some of the earlier telephones the bell capacitor was in the "earthy" (A leg) end of the Bell circuit, this makes it difficult to strap these phones to work on the "modern" plug and socket system without still utilizing the internal ringing capacitor built in to the phone instead of the one fitted in the master line jack.

If your 312 is fitted with a "call exchange" button there may be a rectifier fitted in the phone (in the call exchange switch circuit) that was only used on shared service (party line) working.

Regards
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