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[sevenlayermuddle]

The simplest thing would be for me to test it with and without the resistor.

Arguably, if mine already has a resistor, I could try removing it.  That might be, and I apologise for what I am about to say, the path of least resistance.   

But as for Tuits, mine invariably seem to quickly go pear-shaped these days, so maybe better you do it after all.   

Apols BTW for an empty post a moment ago, not sure how it happened, hope nobody noticed. 

[vic0239]

Information and instructions on converting old telephones to the current system can be found here: http://www.britishtelephones.com/pstconv1.htm, excellent site.

[sevenlayermuddle]

I have had a peek inside my 706.  It has *(see ps) no resistor fitted, and appears to ring and function perfectly.  The common base-station which serves my DECT handsets and answerphone, also appears to ring and function perfectly.   

With reference to the internal picture of a 706 here...

 http://www.britishtelephones.com/tranchan.htm#converted

...the location the 3k3 resistor is fitted (Terminals 4-5) is occupied by an original looking shunt, like the one shunting 5-6.   Marginally off-topic, but then this is a wandering thread... I assume such a resistor would also have been fitted to the phones, to reduce the REN, when an extension was legitimately added to a circuit, hence the removable shunt?  Am I Right? Wrong?


PS Since composing above I have found information stating that some bells were 1k resistance, others were 4k.  Mine is 4k, hence no resistor is needed, which proves nothing in regard to 1k bells.  I actually suspect my phone has not in fact been converted at all, but was probably supplied with modern plug attached in the first place, there was after all an overlap in the technologies.   

[vic0239]

...the location the 3k3 resistor is fitted (Terminals 4-5) is occupied by an original looking shunt, like the one shunting 5-6.   Marginally off-topic, but then this is a wandering thread... I assume such a resistor would also have been fitted to the phones, to reduce the REN, when an extension was legitimately added to a circuit, hence the removable shunt?  Am I Right? Wrong?

Just opened up my 706 from 1962 and I have fitted a resistor across T4-T5, the bell motors being 1000 ohm. You are correct in your assumption of their purpose, but it depends on how the ringing current is supplied whether they are necessary. If each extension socket utilises a filter then each will be capable of providing sufficient current due to the filter having its own capacitor, but if the filtering is centralised there could be an issue with multiple phones of this type connected. Using multiple filters can introduce other annoyances such as bell “tinkle” when dialling from the 706 if you have additional phones like this.

I think the "shunt" between T5-T6 this is just a strap to facilitate connecting varying configurations of the circuit board depending on how the phone was being used.

[sevenlayermuddle]

It would be interesting to know whether there was any significant loudness reduction from the 1k ohm bells, after the 3k3,series resistor was added.   Logically, I'd say there must be a reduction, since the power absorbed by the bell will be less than what was originally intended.   


Similarly of course, were phones that left the factory with 4K bell coils quieter than those with 1K coils?

Edit:  Remove gibberish calculations, shouldn't try to calculate anything after beer.  

[vic0239]

It would be interesting to know whether there was any significant loudness reduction from the 1k ohm bells, after the 3k3,series resistor was added.   

By no means a scientific measurement, but using my own auditory sensors I could not discern any difference in volume when the resistor was removed from the circuit. Certainly nothing to diminish the effectiveness of the bells.

[burakkucat]

With reference to the internal picture of a 706 here...

 http://www.britishtelephones.com/tranchan.htm#converted

I'm surprised I didn't notice it when you first posted the link -- but the picture shows a converted 746, not a 706! Anyhow they are both members of the 700 series. (To state the obvious.)

[sevenlayermuddle]

I'm surprised I didn't notice it when you first posted the link -- but the picture shows a converted 746, not a 706! Anyhow they are both members of the 700 series. (To state the obvious.)

I'm a little confused (some would say 'Yes, we know'    )

But the web page to which I linked has both 706 and 746 'converted' pictures.  For some reason, not understood to me as I am not expert in html, the link opens on my browser at picture of a 746, near end of the page.  But scrolling, up a 706 can be seen above it on the same web page, and that is the picture I was referring to.   

Or am I even more confused that I thought?   

[burakkucat]

The train of events that you have described are exactly that which I experience. (Taking the link opens up the page at the image of the 746.  )

Anyhow, b*cat is also easily confused!

 

[sevenlayermuddle]

Oddly enough, I also have a 746 that I bought in a local antique shop a few years ago.   I had never got around to converting it as I had never got around to figuring out what was needed.   But thanks to this thread, I feel more confident and may well get on with it.

One small problem is that there is no longer full bell-wire continuity between all of my sockets, having been disconnected in an effort to 'optimise' for DSL.   So the phones would (a) need to each have a micro filter for ring signal and (b) would each tinkle, as the other one dialled.

But heck, the bell tinkle will be another nostalgic moment, a familiar sound to many who installed their own extensions that were not entirely 'legit', back in the day.

[burakkucat]

One small problem is that there is no longer full bell-wire continuity between all of my sockets, having been disconnected in an effort to 'optimise' for DSL.   So the phones would (a) need to each have a micro filter for ring signal

A micro filter should not be necessary. Just fit a strap between terminals T17 & T18.

(b) would each tinkle, as the other one dialled.

But heck, the bell tinkle will be another nostalgic moment, a familiar sound to many who installed their own extensions that were not entirely 'legit', back in the day.

Instead of the strap, mentioned above, use a Thermistor 1A-1.

I'll refer you to diagram N846. 

[sevenlayermuddle]

Thanks B*cat.   It should have been obvious that a filter was not a necessity as these phones functioned back in the 1970s, before filters (or even 'master sockets') had appeared.   

I am certain I can find a 3k3 resistor.  And I can probably find a BT lead with plug, that I can cannibalise to make a lead.  I know that I won't find a suitable thermistor in my toy box so that will have to be ordered, although I am sure I can find enough other bits and bobs on my 'want list' to merit an order from Maplin or RS.   

[burakkucat]

If you would like the proper lead, in the right colour, with a 431A plug at one end and the moulded on square grommet at the other end, along with spade connectors for the wires, then have a quick search on eBay. Here's two I found earlier --

Just the line cord. Both the handset cord and the line cord.
 

[sevenlayermuddle]

Yes thanks, I had found the eBay traders.

Whilst I am tempted to do it with proper parts, my 746 phone still has at least the original grommet, unoccupied, that I think I can bodge/modify for whatever old lead I can find.   It won't be as neat as a new lead with correct colours, spade terminals and moulded grommet, but will be better than nothing - at least until I satisfy myself the phone, bell and handset all work.

[sevenlayermuddle]

Slightly embarrassing that it has taken me this long to notice, having declared my 706 as 'working' several days ago, but today I actually used it to conduct a conversation using it... And I found that the sound of my own voice was really quite distracting, 'sidetone', I think it is called.   

From brief research, the 706 was meant to have good anti-sidetone circuitry, for its day.  So the question is, how effective should that be? 

I am not seeking component-level guidance for faults that might cause excessive sidetone, merely general guidance as to what level of sidetone was 'normal', and what level might suggest a fault that merits investigation.