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Old 29th Oct 2009, 11:28 pm   #21
retrotelecom
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Default Re: Another 700 series question

I can feel a quick coming on here!
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Old 29th Oct 2009, 11:44 pm   #22
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Default Re: Another 700 series question

Hi,
The Hook switches on most 700 type telephones are pretty reliable, even after years of use. Two clicks when operating the switch slowly seems to be the norm for these type of switches.

It wouldn't hurt to check the continuity of the switch contacts with a meter though just as a precautionary measure, with straps T4, T5, T6 removed you should have a short circuit reading across T5 - T6 with the phone in On Hook condition, changing to a short circuit between T5 - T2 when Off Hook.

Similarly you should have an open circuit Between T19 - T3 when On Hook, changing to around 22 to 40 Ohms when Off Hook. Checking in this way saves you having to remove the printed wiring board.

As long as the resistance between T19 - T3 isn't massive (over a few hundred Ohms, which it shouldn't be anywhere near due to the absence of the regulator) and is no less than 22 Ohms, Your Hook switch is fine.

It may be prudent to remove the handset cord when carrying out these checks to avoid false readings.

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Andrew
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Old 30th Oct 2009, 12:17 am   #23
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Default Re: Another 700 series question

Out of interest, is there any chance of a photo of the bell-motor? The bobbins and armature don't seem to be where they should be, and I am just curious...

It hasn't got owt daft on it like a DC bell, has it?
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Old 30th Oct 2009, 1:46 am   #24
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Default Re: Another 700 series question

OK. Thanks Nick - I'll get on to that in the morning.
Russell - I think you may have hit on another twist to the story there - here's the pic
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Old 30th Oct 2009, 1:51 am   #25
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Default Re: Another 700 series question

Does anyone want to take this 'phone off me??!!
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Old 30th Oct 2009, 9:28 am   #26
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Default Re: Another 700 series question

Quote:
Originally Posted by retrotelecom View Post
'Russell - I think you may have hit on another twist to the story there'
It's an AC bell, but one that replaced the type 59A (the traditional two-bobbin type, of which there were several variants). I once bought several of these newer bell-motors surplus! The polarising magnet is visible at the back, and it is stamped '1000 Ohm'. I think it is known as a type 79A, like the one fitted to bellset (and compact telephone) 776.

My goodness! It looks like you have a parts-bin special! It might be worth a fortune .
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Old 30th Oct 2009, 11:36 am   #27
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Default Re: Another 700 series question

Quote:
Originally Posted by russell_w_b View Post
It's an AC bell, but one that replaced the type 59A (the traditional two-bobbin type, of which there were several variants). I once bought several of these newer bell-motors surplus! The polarising magnet is visible at the back, and it is stamped '1000 Ohm'. I think it is known as a type 79A, like the one fitted to bellset (and compact telephone) 776.
...and the Ambassador? A 1950s design full of bits that wouldn't be out of place in an early-1980s phone.

Quote:
Originally Posted by russell_w_b View Post
It might be worth a fortune .
Probably not (yet), but it's certainly rare!

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Old 30th Oct 2009, 11:42 am   #28
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Default Re: Another 700 series question

Quote:
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Does anyone want to take this 'phone off me??!!
I'll have it if you're literally giving it away, but don't give up yet, I think you're nearly there
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Old 30th Oct 2009, 1:00 pm   #29
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Default Re: Another 700 series question

OK. I won't give up yet - I might be rich!
Switch readings as follows:
hansdset removed, links T4, T5, T6 removed
T5 - T6 on hook - short circuit
T5 - T2 off hook - open circuit
T19 - T3 off hook - open circuit
T19 - T3 on hook - open circuit
one thing I forget to mention - when I ring into the 'phone - no ringing on hook, but loud "ring tone" in handset when off hook
I didn't understand the Ambassador reference??
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Old 30th Oct 2009, 2:04 pm   #30
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Default Re: Another 700 series question

Quote:
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'I didn't understand the Ambassador reference??'
The Ambassador is a telephone that shares the same bell-set. It appeared around the transition between the Public GPO and the private BT.
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Old 30th Oct 2009, 2:44 pm   #31
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Default Re: Another 700 series question

Yes, it was an early 1980s (?) phone, more often found in offices than at home, see here: http://www.britishtelephones.com/ambassa2.htm

N.
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Old 30th Oct 2009, 2:55 pm   #32
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Default Re: Another 700 series question

I should have known. For my sins in life I actually have one - bought at a car boot - brand spanking new, in box, and the most fowl 'chocolate' for want of a better word, brown colour. Not the prettiest thing in the world, but I guess in a hundred years time, it will be rare. My grand-kids will thank me one day!
Doug
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Old 30th Oct 2009, 7:05 pm   #33
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Default Re: Another 700 series question

Quote:
Originally Posted by retrotelecom View Post
Switch readings as follows:
T19 - T3 off hook - open circuit
T19 - T3 on hook - open circuit
Hi,
The above reading suggest that your problem may be an open circuit induction coil (or broken print tracks on the board) this would certainly give the transmission symptoms that you are experiencing, and may also be contributing to the "Ringing" fault too.

When there is no regulator fitted there are points that need to be shorted together, where the regulator should be fitted, to maintain loop continuity; If you can work out on your board the equivalent of Points B, C and D (as per the 706 N Diagram) make sure that these points are shorted together - if these points are not shorted together you will get the symptoms that an open circuit induction coil would cause as mentioned above.

Regards
Andrew
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Old 30th Oct 2009, 8:22 pm   #34
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Default Re: Another 700 series question

Well. I figured, looking at the diagrams, that B on the non present regulator can be picked at T3, C is connected to pin 5 on the coil, D to pin 1 on the coil. So I shorted out coil pin 5 and T3. BINGO ... dial tone and microphone. Shorting coil pins 5 and 1 as well made the dial tone ever so slightly louder. Dial tone is quiet though and the mic seems lively - but some progress!! Still no bells.
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Old 30th Oct 2009, 8:57 pm   #35
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Default Re: Another 700 series question

Hi,
The induction coil Pins 1 and 5 must be connected together and both taken to T3 (the equivalent of point B) for transmission to function correctly.

The quiet dial tone may be a combination of a lack of regulator and your distance from the exchange.

Looking at your pictures of the printed board there does seem to be holes pre-drilled for a fixed regulator and associated components, if you remove the board you could always solder links at the appropriate points to make a neater job than connecting wires on the top side of the board.

Regarding the bell have you added strap T17 - T18 as mentioned in one of my earlier posts? if you have there is a possibility that the bell coil is open circuit, I have had this a few times and it seems more common with the type of bell coil that you have than with the older dual coil versions (unusually).

If the bell coil is found to be faulty the mounting screw holes are in the same place on all types of 700 telephone bell; if you do need to replace the coils try to obtain 4K ones which means that you can dispense with the resistor across T4 - T5 (and re-fit the strap)

Regards
Andrew
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Old 30th Oct 2009, 9:30 pm   #36
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Default Re: Another 700 series question

Hi. Woah! We're getting there. Quiet dial tone must be lack of regulator then, because I can actually see the telephone exchange from here!
I added link 17/18 (misreading your instuction) ... and the bells began!! So, I think - it's working. I'll set to and do the neater wiring that you suggest. Not entirely what I'm going to do with it now it works!

Doug
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Old 30th Oct 2009, 9:43 pm   #37
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Default Re: Another 700 series question

Hi,
If you are close to the exchange I would have expected the dial tone to be loud and not quiet if a regulator is not fitted, others may be able to confirm this for definite.

As you are now confident that the phone has basic transmission operation it might be worth fitting a regulator if you intend to put the phone in to regular use; As the holes are already there for a regulator and "lamps" (thermistors) and you will have to remove the printed board to tidy up the wiring so why not try and obtain a regulator etc. from a salvaged 746 board and fit them anyway?

Well done with your efforts so far

Andrew
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Old 30th Oct 2009, 10:08 pm   #38
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Default Re: Another 700 series question

Well, thanks to you Nick for doing all the hard work really - and to Russell and all others who helped.
I think it may well be worth "going the extra mile" now, and sort out a regulator etc. Might as well finish the job off properly, eh?
Quick suggestions for source of such things? I guess ebay, telephonelines.com, ??

I'll let you know if it still works after I've been at it with a solering iron!!

Cheers
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Old 30th Oct 2009, 10:18 pm   #39
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Default Re: Another 700 series question

Sorry! I meant Andrew. It's addled me brain, this one 'as.
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Old 30th Oct 2009, 10:34 pm   #40
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Default Re: Another 700 series question

Might as well stick this (hopefully) last Q in on this thread. I've been doing all this away from home without the aid of a landline in my digs. I've been 'borrowing' a friend of a friends line down the road. I spend a fair bit of time away from a landline, but don't want to lose that time for meddling with phones. I've seen a linesman Tele 286A. Would that provide me with line conditions, ring current etc??
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