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Old 14th Jun 2012, 10:27 pm   #21
boombox
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Default Re: 1920s Direct line telephone/intercom

Hmmm - no joy. Tried to gently shake the mic and I think I could hear loose granules so that can't be the problem.

So now I have them wired correctly with 1.5v for the mic and 4.5v for the bells. The bells work but the mic/earpieces don't.

Curiously when the button is pressed on one unit and the receiver is off hook on the other, whilst speech isn't transmitted the magnets in the receiver do activate the diagphram because they click and "the sound of the sea" can be heard.

Does anyone here have an interest in or specialise in repairing these? I really would like to see them working! whilst I would prefer them to sound authentic if no spare period mics/speakers are available is replacing parts with more modern components an option?
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Old 15th Jun 2012, 4:51 pm   #22
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Default Re: 1920s Direct line telephone/intercom

Those symptoms don't sound quite right.

The connections quoted in the Britishtelephones link in your earlier post seem to be correct for your 4 wire Phoenix house phone, so I would use these, at least initially (pasted below for convenience)
Pushing either call button should ring the other phone's bell. You seem to be OK here. Lifting both "hooks" establishes the speech path, for which neither call button should be pushed.

Wiring two Telephones together
Each telephone requires three 1.5 volt batteries.
The phones are connected together by two wires.

At each telephone connect the batteries as follows:-
1. Connect the three batteries in series.
2. Connect the free negative terminal of the battery set to terminal ZE
on the phone.
3. Connect the free positive terminal of the battery set to terminal C
on the phone.
4. Connect the positive terminal of the centre battery to terminal MC
on the phone.

Connect the two phones as follows:-
1. Connect terminal ZE of one phone to terminal ZE of the other.
2. Connect terminal L of one phone to terminal L of the other.

Try this and report back with your findings.
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Old 15th Jun 2012, 7:46 pm   #23
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Default Re: 1920s Direct line telephone/intercom

You say the positive terminator of the centre battery? So 3v for speech and 4.5v for the bell? Elsewhere I've read 1.5v for MC and 4.5v for C.

But that's fine - I tried it, and same result as before (when I was using 1.5v for MC and 4.5v for C).

Do we think it might be the microphones?
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Old 15th Jun 2012, 8:45 pm   #24
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Default Re: 1920s Direct line telephone/intercom

There are three active components in each phone. Microphone, earpiece and transformer.
Any one of them could be problematic, but if both ways are affected it points to an age related fault, which is not really surprising after the best part of a Century.

The earpiece magnets could be weak by now, or the carbon granules may be degraded in some way. They can both be substituted by a (more) modern part in an attempt to narrow it down. I wouldn't suspect both transformers, but you never know.

I think that the carbon granules were available to revitalise microphones, but I wouldn't think they are now, assuming that the microphone can be opened. If so, you could try baking them as suggested earlier.
You could also try reversing the earpiece diaphragm, they tend to sag over the years.
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Old 18th Jun 2012, 10:50 am   #25
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Default Re: 1920s Direct line telephone/intercom

Hi - I can't see that baking was suggested earlier in thread but it's an interesting thought I might try some day!

As things stand, I've made some headway.

I substituted the original carbon microphone with an electret one from my 746 telephone. At first this didn't seem to work either but when I removed the tap and supplied the new mic with 4.6v it activated and worked. The thing is there is either something wrong with the mic circuitry or the receiver circuitry one one of the units because I can only communicate in one direction at the moment. I've tried the earpiece from my 746 and that doesn't resolve the problem (whereas it does work fine on one unit).

Thanks & regards
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Old 18th Jun 2012, 5:27 pm   #26
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Default Re: 1920s Direct line telephone/intercom

If I read this correctly you've got one way transmission using a replacement transmitter and a replacement receiver. If you swap each one to the other phone does it work in the reverse direction?.
I've opened my microphone, and it has a sealed insert No.3 like this one
http://www.richardsradios.co.uk/phoenixmic.html
so it will probably not be repairable.
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Old 18th Jun 2012, 6:19 pm   #27
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Default Re: 1920s Direct line telephone/intercom

That's the thing. It works one way. If I swap them over, it doesn't work in the other direction. There must be a wiring/coil fault somewhere.
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Old 18th Jun 2012, 11:49 pm   #28
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Default Re: 1920s Direct line telephone/intercom

You can see the wiring, it's so simple. Looks like there could be a faulty transformer after all. Can you measure continuity on the windings and compare them?
In any case you have at least two problems, a transmitter and a receiver.
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Old 19th Jun 2012, 12:17 am   #29
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Default Re: 1920s Direct line telephone/intercom

Even if one of the transformers has an open-circuit winding, it shouldn't be too hard to rewind it. You know one of them is fine, so get out your meter (200Ω range) and compare the two like-for-like.
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Old 19th Jun 2012, 1:42 pm   #30
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Default Re: 1920s Direct line telephone/intercom

I did compare the coils on Sunday evening and noticed that the coil on the none working unit has continuity on windings the working unit's does not.

I can be more specific, I realise this isn't exactly specific.

I'm not familar with how to rewind a coil, but I am willing to learn and give it a go.

As for having at least two problems, I think I have:
1) A non-working microphone on one unit
2) Faulty coil (and possibly non-working mic/receiver as well) on the other.

Thanks
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Old 19th Jun 2012, 3:00 pm   #31
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Default Re: 1920s Direct line telephone/intercom

If you wire a carbon microphone (the suspected good one) in series with a 3V battery and a earpiece (a working one), then you should hear sounds from the earpiece when you speak into the microphone. Then swap in the suspect microphone instead and see if it stops working.
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Old 19th Jun 2012, 3:22 pm   #32
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Default Re: 1920s Direct line telephone/intercom

Quote:
Originally Posted by boombox View Post
I did compare the coils on Sunday evening and noticed that the coil on the none working unit has continuity on windings the working unit's does not.
Are you sure it's that way round. I would expect to have continuity on the working coil.
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Old 19th Jun 2012, 7:07 pm   #33
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Default Re: 1920s Direct line telephone/intercom

If all else fails, as long as you can persuade a working microphone and receiver to fit into each phone, you can wire them as post 14 (3 wire). The coil was only used to increase the range, which you probably don't need. There might be a bit more sidetone, but it will work OK.
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Old 15th Feb 2014, 5:21 pm   #34
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Default Re: 1920s Direct line telephone/intercom

Would anyone like to bid on getting these working again? I'm talking about a 'paid for' job.

Working means:-

-2 way speech
-Working ringing on each

I will handle the refurbishment myself.

I don't have the time (and would need to acquire the skill!)

Thanks
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Old 16th Feb 2014, 2:53 pm   #35
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Default Re: 1920s Direct line telephone/intercom

As this request is now here https://www.vintage-radio.net/forum/...d.php?t=103776 I'm closing this thread.
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