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Old 6th May 2019, 5:52 pm   #1
SimonF114
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Default WW2 British ‘L’ Field Telephones.

Hi all,

New member, thanks for the add!
I don’t know much about electronics, but here to learn

I recently got from the local car boot, two WW2 British ‘L’ field Telephones. One in somewhat rough condition dated 1941, the better one 1944. I’ve thoroughly cleaned the contacts, re-soldered some of the perished wires and added D size battery holders, and they work great.

My question for the experts - although I can have a conversation between the two phones, talking into the microphone in the handset of the ‘1944’ phone, is very quiet when listening on the other phone. I swapped over handsets between the telephone units (‘1944’ handset in the ‘1941’ unit, and vice versa), to make sure there isn’t a potential problem in the ‘1944’ telephone unit. It’s still the same problem on the same handset.
Would anyone know what would cause the microphone to be quiet? I’ve tried to take the Bakelite mouthpiece off the handset to have a look at the microphone, but I can’t for the life of me see how is comes off!

Many thanks for your patience for a newbie.

Best regards,

Simon
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Old 6th May 2019, 6:34 pm   #2
trh01uk
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Default Re: WW2 British ‘L’ Field Telephones.

You say you have added a D size battery holder. How many cells does that have? One, two.....?

I can't recall how many cells they used originally, but if you haven't got enough volts to power the microphone, then that might well explain why they are bit quiet. No doubt an expert on these with the manual will pop up and tell us exactly how many primary cells were needed. As I recall they were square in cross-section last time I used these things (about 38 years ago!)

Richard
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Old 6th May 2019, 6:39 pm   #3
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Default Re: WW2 British ‘L’ Field Telephones.

The other comment I would make on these is that they use carbon microphone inserts and the carbon granules in them tend to clump together and stop working as efficiently as when new. Supposedly, some hard knocks on a wooden table will free said granules, but I can't speak for how well that will work. Worth a try!

Richard
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Old 6th May 2019, 7:00 pm   #4
Dave Moll
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Default Re: WW2 British ‘L’ Field Telephones.

They run on 2x No.12 batteries, for which a pair of either "C" or "D" cells are a suitable substitute.

Regarding the problem of the quiet sound, I take it that the handsets have been swapped as a whole (by unplugging them at the four-pronged plugs). If this is the case, the problem may either lie in the receiver (earpiece) of the quiet one, or (more likely) the transmitter (microphone) of the other one.

Is the sound simply quiet or is it also distorted? The latter would confirm the problem is with the transmitter, owing to the carbon granules not responding to the pressure waves of the speech. This can sometimes be improved by taking out the transmitter inset (by inserting a pointed tool into the small hole in the side of the mouthpiece cover while twisting this cover slightly anti-clockwise) and giving the inset a few firm (but fairly gentle) taps against a solid surface to free any clogged granules.

If a conclusion cannot be reached as described above, the way to confirm whether the problem lies with a transmitter or a receiver is to swap the transmitter insets between the two handsets and see whether the problem migrates.

Edit: for some reason, Richard's second reply didn't appear until I posted mine.
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Old 6th May 2019, 7:57 pm   #5
OscarFoxtrot
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Default Re: WW2 British ‘L’ Field Telephones.

I don't know if they're the same as ordinary GPO and similar handsets, but if there's a hole in the circumference of the mouthpiece, "inside" the handset, put a blunt nail into it and press firmly, and that will release the bayonet lock on the mouthpiece cap with will then untwist.
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Old 6th May 2019, 8:13 pm   #6
Dave Moll
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Default Re: WW2 British ‘L’ Field Telephones.

Although the 184 handset in field telephones uses a different mouthpiece cap from the 164 GPO handset, the same arrangement of bayonet lock is employed.
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Old 6th May 2019, 9:18 pm   #7
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Default Re: WW2 British ‘L’ Field Telephones.

you should be able to hear the granules rattling when you shake the microphone. Quite possible they've got damp with something.

While the mic's out, check the resistance of the flex, and I think these have a push to talk switch, make sure it's contacts are ok.
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Old 7th May 2019, 12:20 am   #8
SimonF114
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Default Re: WW2 British ‘L’ Field Telephones.

Hi all,
thanks very much for the replies.
Spent the evening fiddling around with them, following the replies.

@Richard, I put in a double 'D' battery holder, as I found out along the grapevine about the original batteries being 1.5V each.

@Dave, Indeed, I swapped them as a whole, and it was just simply quiet/low volume. Thanks for the description of how to gain access to the transmitter, and of the granules inside it (Simple when one knows how! lol). I gave both transmitters a gentle tap, and the granules sound much more free, as well as a gentle clean of the contacts (Bit grubby, like the rest of the phone was).

@McMurdo, I also gave the switches an inspection. only one wire had had it, and I replaced, but are good contacts.

I wired the phones up again, tested them, and the sound in both phones have much more clarity, and is no longer quiet.
I do WW2 exhibitions showing some of my military collection. I pride all of my collection with 'fully working' artefacts.

Many thanks for the help - an excellent and helpful resource!

Best regards,

Simon
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Old 7th May 2019, 8:43 am   #9
Dave Moll
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Default Re: WW2 British ‘L’ Field Telephones.

Good to know that you have the problem sorted. Although it's possible to substitute an electronic 21A transmitter inset (as long as you up the battery to at least 4½V), it's so much better to keep it original.
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Old 15th May 2019, 8:12 am   #10
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Default Re: WW2 British ‘L’ Field Telephones.

Hello all.
I have a number of these field phones here.
Some were used by the Postmaster Generals Office (PMG) to help maintain the phone network. Some of these were fitted with a rotary dial.
I also have a couple that look the same as a type "L" phone but are sound powered and do not have a battery or a battery box.
Cheers, Robert.
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Old 15th May 2019, 11:06 am   #11
Dave Moll
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Default Re: WW2 British ‘L’ Field Telephones.

Quote:
Originally Posted by QQVO6/40 View Post
I also have a couple that look the same as a type "L" phone but are sound powered and do not have a battery or a battery box.
Cheers, Robert.
I assume those are Telephone Set "H" (Mk3?) then. The Mk2 looks more like a Telephone Set "F". I have one of each.
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Old 15th May 2019, 1:42 pm   #12
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Default Re: WW2 British ‘L’ Field Telephones.

Hello all.
Thanks for that Dave.
Tels (H). I must remember that. Next time I get near them I will confirm that but you will be correct.
I have not seen those phones for a while as I have too much "stuff".
As I remember they look almost identical to the Tels "L" except for the lack of a battery box.
I have a few of the ex PMG (Post Master Generals Department) phones that look identical to the Tels (L) except for the door on the left hand side to the left of the battery box. Under the lid is a standard rotary dial.
Not a bad phone to use actually. It will work on manual, CB or auto.
The batteries are still used to power the microphone circuit.
Cheers, Robert.
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Old 15th May 2019, 4:09 pm   #13
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Default Re: WW2 British ‘L’ Field Telephones.

Quote:
Originally Posted by QQVO6/40 View Post
Hello all.
Thanks for that Dave.
Tels (H). I must remember that. Next time I get near them I will confirm that but you will be correct.
I have not seen those phones for a while as I have too much "stuff".
As I remember they look almost identical to the Tels "L" except for the lack of a battery box.
I have a few of the ex PMG (Post Master Generals Department) phones that look identical to the Tels (L) except for the door on the left hand side to the left of the battery box. Under the lid is a standard rotary dial.
Not a bad phone to use actually. It will work on manual, CB or auto.
The batteries are still used to power the microphone circuit.
Cheers, Robert.
See https://britishtelephones.com/ericsson/n1845.htm for the non-military versions.

Ian
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Old 15th May 2019, 7:58 pm   #14
Dave Moll
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Default Re: WW2 British ‘L’ Field Telephones.

Here are my "H" sets:
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