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Old 30th Apr 2014, 10:49 am   #1
barriejohn
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Default World War II field telephones.

I have recently aquired a World War II field telephone (Type F MkII).

Does anyone know if it is possible to convert these to accept incoming calls from a BT line?

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Old 30th Apr 2014, 12:52 pm   #2
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Default Re: World War II field telephones.

Possible? Yes. There's probably room inside to hide the circuit from a standard phone in some format and just feed the handset and cradle switch as the only original bits of the phone to be used. You would likely need to get inventive to operate the buzzer from the line, though, so easier to go with an external bell set or just another normal phone on the line.

There's a circuit of the Tele F II here: https://www.vintage-radio.net/forum/...50&postcount=3
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Old 30th Apr 2014, 2:59 pm   #3
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Default Re: World War II field telephones.

It'll work if you just connect L1 and L2 to the incoming pair (or terminals 2 and 5 in the BT socket), as long as you have a battery connected inside to work the mic.

Don't turn the magneto, though, as you'll simulate dial pulsing and could easily end up calling 112 (emergency services)! You might like to put a 3k resistor in series with the bell motor to increase the REN as well. It's just a 59A type ringer, same as in a 336 or 706 instrument. The speech quality won't be brilliant. I have a feeling the carbon mic insert for field telephones is not quite the same as a 'Mic, Inset No:13' used on 300 or 700 series instruments, being optimised for 3V local battery excitation.
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Last edited by russell_w_b; 30th Apr 2014 at 3:05 pm. Reason: Extra stuff added.
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Old 30th Apr 2014, 3:11 pm   #4
Dave Moll
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Default Re: World War II field telephones.

Quote:
Originally Posted by Herald1360 View Post
You would likely need to get inventive to operate the buzzer from the line, though, so easier to go with an external bell set or just another normal phone on the line.
As the telephone "F" has an integral bell, ringing on incoming calls should not be a problem. Even if your set has a buzzer, and not all Fs do, it's probably best to ignore this as well as the magneto, as it may also create unwelcome effects on the telephone network.

As a disclaimer, I should probably say that such connection would definitely be frowned upon by the network management!
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Old 1st May 2014, 3:03 pm   #5
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Default Re: World War II field telephones.

Quote:
Originally Posted by russell_w_b View Post
I have a feeling the carbon mic insert for field telephones is not quite the same as a 'Mic, Inset No:13' used on 300 or 700 series instruments, being optimised for 3V local battery excitation.
GPO Teles used 3 or 4.5 volts - see N806 page 4 notes. I well remember using both 3XX types and 706's on GPO local battery exchanges - the subs battery box usually had two or three R40 dry cells or the glass leclanche cells - the time spent topping cells up and fitting new zinc rods! Shouldn't be a problem fitting a replacement Transmitter Inset using a GPO one if needs be. I'd also tend to disconnect the wire from the end of the magneto opposite the contacts to save the 75+ volts AC going back to the exchange. Could even go further once that has been done by strapping the three contacts together on the other end of the magneto - thus the magneto would be out of circuit but phone could be restored to original if need be.
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Old 4th May 2014, 9:20 pm   #6
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Default Re: World War II field telephones.

Comment received from a non forum member:-

Quote:
My comment is that "if the tele F has a buzzer it is well to wind back the two knobs so as to clear the contacts. This is because if they are both in contact it shorts out the buzzer winding that causes a severe loss of speech power". Shorted turns on any transformer have the same effect.
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Old 1st Apr 2015, 8:29 pm   #7
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Default Re: World War II field telephones.

this may be an sfq but how does one get at the microphone in the handset? it doesn't twist off like the ear piece. Do I need to depress that metal part I can see in the small hole?
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Old 1st Apr 2015, 8:52 pm   #8
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Default Re: World War II field telephones.

Got it in one. It'll then turn anti-clockwise a few degrees and lift clear — rather like a light-bulb.

- Joe
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Old 1st Apr 2015, 8:55 pm   #9
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Default Re: World War II field telephones.

Quote:
Originally Posted by 50sqnwopag View Post
Do I need to depress that metal part I can see in the small hole?
Better asking a sfq now than making a sfm later!

You are correct. Stick a drawing pin or what-have-you in the hole and twist off anti-clockwise, less than 90 degrees. The mouthpiece is a bayonet fit, same as on a type 164 (or 184) handset as used on GPO bakelite instruments.
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Old 2nd Apr 2015, 11:07 am   #10
50sqnwopag
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Default Re: World War II field telephones.

tar will give it a go
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Old 2nd Apr 2015, 9:30 pm   #11
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Default Re: World War II field telephones.

The pin on a standard handcuff key used for double-locking the handcuff is excellent for the purpose of releasing the mouthpiece on a Handset 164.

http://www.britishtelephones.com/t164.htm
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