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Old 21st Dec 2009, 1:03 am   #1
Alf
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Default Army Field Telephones and Compatibility?

Are they compatible with each other? For instance, would a telephone set type "H" MkIII be compatible with, say, a type "L." There's obvious differences in the circuitry with many field telephones. What I'm asking, is, can you connect different types together? Would a type "H" only work ok with another type "H?" A type "L" with another type "L?"

As an aside, the field telephone I have has a rigid magneto handle, there's no "slip" on the handle, is this normal? On other magneto phones I have, the bit of plastic/bakelite on the handle turns freely.
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Old 21st Dec 2009, 9:18 am   #2
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Default Re: Army Field Telephones and Compatibility?

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Are they compatible with each other?
As long as the signalling circuit works, then yes. You can only call a type F from a type D using DC signalling (buzzer). But you can call a type D from a type F using either buzzer or magneto, because a D has a magneto bell as well as a buzzer.

You can call any magneto telephone from any magneto telephone, and you ought to be able to speak, as the mic circuitry is internal to the telephone, being presented as an AC voice signal at the terminals (or should be). Chech that there's no DC at the terminals when the handset is lifted and / or the pressel switch is made.

A Soviet TAI-43 will work satisfactorily with a UK / Commonwealth type F, I've found.
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Old 21st Dec 2009, 9:35 am   #3
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Default Re: Army Field Telephones and Compatibility?

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'As an aside, the field telephone I have has a rigid magneto handle, there's no "slip" on the handle, is this normal? On other magneto phones I have, the bit of plastic/bakelite on the handle turns freely.'
You mean your fingers always want to move when you crank?

I've never seen a rigid knob on a handle; it seems to be designed to allow cranking whilst preventing one's fingers from slipping off. Could you remove the handle from the generator and soak them in oil overnight before attempting to unscrew the knob from the handle?
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Old 21st Dec 2009, 10:10 am   #4
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Default Re: Army Field Telephones and Compatibility?

I've been wondering about this too.

I haven't been able to find any web sites that document what all the different systems are and which models do what. What's the best source of such information?

Also, from what you said about a/c only on the line, does this mean that the non-powered models can still work with the regular kind?
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Old 21st Dec 2009, 11:30 am   #5
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Default Re: Army Field Telephones and Compatibility?

I've had no difficulty getting any of my field telephones to talk (or signal) to each other. Even the German ones talk with the British ones - something they probably wouldn't have been expecting to do

Although I'm not familiar with non-powered field telephones, I do have a wooden wall telephone which communicates OK with the field telephones as long as I supply it with power from an external battery - though its DC trembler bell isn't compatible.
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Old 21st Dec 2009, 1:59 pm   #6
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Default Re: Army Field Telephones and Compatibility?

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Also, from what you said about a/c only on the line, does this mean that the non-powered models can still work with the regular kind?
Maybe...

Presumably you mean 'sound-powered' models, like the magneto-signalling steel wall-mounted type as used on ships? These sort will have a balanced (rocking) armature receiver and a similar transmitter, rather than a DC-powered carbon microphone.

Now, some models of powered field-telephone were retro-fitted with rocking-armature receiver inserts, either of the type 'Receiver, Inset, 4T' (the type of thing one finds in a 706 or a 746 instrument), or of the type found in DLR5 headphones. Both modifications are easily spotted because the earpiece is attached to the handset via a threaded aluminium notched ring holding a bakelite receptacle in place to accommodate the BA receiver. The receptacle takes the receiver electrical contact screws that would've held the original 2P or 1L receivers in position.

I'm guessing that a battery-less sound-powered unit will work satisfactorily with one of these modified battery-powered instruments (typically a type F would have a DLR5 balanced-armature receiver fitted, and a type J would have an inset, 4T receiver fitted) because of the increased sensitivity of the BA inserts, but I wouldn't think talking into the BA transmitter of a sound-powered instrument would be sufficient to energise the more traditional 2P or 1L receiver inserts (identical to the receiver inserts of a 300 or 200 series bakelite telephone).

Why not try it and let us all know?

The
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Old 21st Dec 2009, 11:45 pm   #7
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Default Re: Army Field Telephones and Compatibility?

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'Also, from what you said about a/c only on the line, does this mean that the non-powered models can still work with the regular kind?'
When you say 'non-powered' models, do you mean the sound-powered kind shown below? Made by the TMC in Dulwich for use by Allied forces during WWII.
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Old 22nd Dec 2009, 12:01 am   #8
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Default Re: Army Field Telephones and Compatibility?

I don't know much about these things. I just know that there are several models that don't need batteries for voice transmission.

Type "H" for example??
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Old 22nd Dec 2009, 2:22 am   #9
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Default Re: Army Field Telephones and Compatibility?

Thanks for the input guys. I'll look out for another field phone shortly, got to get Christmas over first.

I've never seen a rigid knob on a handle; it seems to be designed to allow cranking whilst preventing one's fingers from slipping off. Could you remove the handle from the generator and soak them in oil overnight before attempting to unscrew the knob from the handle?

The handle can be removed from the magneto, what can't be removed, is the small knob at the end, a generous spraying of WD40 has produced no results, there's a screw in the centre that's defying all attempts to loosen it.
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Old 22nd Dec 2009, 8:42 am   #10
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Default Re: Army Field Telephones and Compatibility?

Just based on experience.
To receive a ring signal from a hand cranked telephone, the other end need to have a ringer device to receive this 15-25Hz signal, and transfer it to sound.
To receive a beep, you need a telephone with the receiver in the circuit, even in on-hook condition.

Eg. I have a S.T.C handset. (everything inside the handset) This may not receive the handcranked signal from an US TA 46 / TA 312 and the US TA 46 / TA 312 cant receive the beep if the handset rests on the cradle.

Most others works well together.

Soundpowered telephones e.g. Ta1/PT rings, magneto, and receives everything.
Speaking to a regular batterypowered telephone makes weak signal in the battery operated telephone, but extremely strong signal the opposite direction.

Modern digital terminals? Never used one.

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Old 22nd Dec 2009, 1:52 pm   #11
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Default Re: Army Field Telephones and Compatibility?

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The handle can be removed from the magneto, what can't be removed, is the small knob at the end, a generous spraying of WD40 has produced no results, there's a screw in the centre that's defying all attempts to loosen it.

Thinking about the rotation of the handle relative to its shaft, is it possible that a retaining screw might have a left hand thread (to prevent its coming undone in normal operation?). Also, try Plus Gas instead of WD40, WD40 isn't really a releasing fluid, it's a Water Dispersing agent with a bit of oil in it.


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Old 22nd Dec 2009, 9:23 pm   #12
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Default Re: Army Field Telephones and Compatibility?

One word of caution when using 'buzzer' signalling phones with 'magneto' signalling ones. I have tried a Model D (buzzer ringing) with a Model F (magneto ringing) and they work well, except when the buzzer key is pressed on the Model D during a call. The buzzer note that emanates from the receiver of the Model F is deafeningly loud ...a feature that so amused a group of Scouts recently that I had to revert to a pair of Model Fs on Health and Safety grounds, to prevent hearing damage!

Does this happen when using a pair of Model Ds, or is mine faulty? These are equipped with both buzzer and bell so clearly they were designed to be inter-operable with other types of ringing system. Perhaps the buzzer was supposed to be disabled off-hook, but I've read somewhere that the miniature Morse key was designed for sending messages by Morse Code when battlefield noise was too great for voice traffic to be heard.
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Old 22nd Dec 2009, 9:29 pm   #13
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Default Re: Army Field Telephones and Compatibility?

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I haven't been able to find any web sites that document what all the different systems are and which models do what. What's the best source of such information?
The WS19 Group http://www.royalsignals.org.uk/ holds a vast archive of military radio, communications and electronics information, including field telephones and exchanges. You have to apply to join (no cost) and requesting the information is a bit tortuous, but it arrives by e-mail as a password-protected PDF and it's well worth it.
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Old 23rd Dec 2009, 9:48 am   #14
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Default Re: Army Field Telephones and Compatibility?

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The buzzer note that emanates from the receiver of the Model F is deafeningly loud
I've got a couple of Model Fs in the loft which I used to play with as a child. At least one of them has a buzzer fitted and yes, pressing the 'buzz' button did have a tendency to deafen whoever was at the other end of the line.
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Old 23rd Dec 2009, 1:32 pm   #15
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Default Re: Army Field Telephones and Compatibility?

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...a feature that so amused a group of Scouts recently that I had to revert to a pair of Model Fs on Health and Safety grounds, to prevent hearing damage!
I'm surprised that reverting to a pair of Fs solved the "problem". I find the sound equally deafening between an F and a D and two Fs.

Surely, it's supposed to be loud so that the buzzer sound is audible from a distance with the handset on-hook.
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Old 23rd Dec 2009, 1:42 pm   #16
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Default Re: Army Field Telephones and Compatibility?

A further thought - model D and Model F use the same buzzer unit, so maybe it's the adjustment (using the two knobs on the top) that makes the difference. Maybe the H&S concerns could be addressed by adjusting the buzzers away from their maximum setting.
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Old 23rd Dec 2009, 8:08 pm   #17
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Default Re: Army Field Telephones and Compatibility?

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'Maybe the H&S concerns could be addressed by adjusting the buzzers away from their maximum setting.'
Do remember that type Ds were for use in battle conditions (hence the pressel switch: operable in any position), and H&S would also have to be aware of ambient background noise from bursting shells and machine-gunnery.

Perhaps an instructive talk prior to use (method-statement, risk-assessment and all that...)?
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Old 24th Dec 2009, 8:26 pm   #18
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Default Re: Army Field Telephones and Compatibility?

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I'm surprised that reverting to a pair of Fs solved the "problem". I find the sound equally deafening between an F and a D and two Fs... Surely, it's supposed to be loud so that the buzzer sound is audible from a distance with the handset on-hook.
Sorry, I should have explained that both my Model F phones have induction coils and magnetos and bells, not buzzers.

Agreed about the buzzer sound needing to be loud when on-hook, but when off-hook, should it be silenced or muted to a safe level?
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Old 24th Dec 2009, 10:05 pm   #19
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Default Re: Army Field Telephones and Compatibility?

Now I understand - the buzzer is optional on the "F", because it also has a magneto, whereas the buzzer is the only means of signalling from the "D".

It would have been difficult to alter the sound level of the buzzer when the receiving unit goes off-hook as the sound level is determined by the transmitting unit. Reducing the level at the receiver would also reduce the volume of speech received. The only way it could have been achieved would be for the transmitter to use the drop in line impedence created by the receiver's off-hook condition to reduce the output level from the buzzer. I guess that this complication was either considered not worthwhile or not considered at all.
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Old 25th Dec 2009, 8:41 pm   #20
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Default Re: Army Field Telephones and Compatibility?

I was thinking more along the lines of the buzzer being disabled when the receiver was off-hook, thus preventing loud buzzer tone from actually being transmitted during a call. It's an academic point now, of course! I was just interested in confirming that my phones were not faulty, which seems to be the case.
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