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Old 25th Dec 2009, 11:54 pm   #21
GMB
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Default Re: Army Field Telephones and Compatibility?

Some clarification required here:

I just found the circuit of a Type D and it shows a buzzer and a bell but no magneto.

Also, what a/c voltage does the magneto ringer generate e.g. on a Type F?
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Old 25th Dec 2009, 11:56 pm   #22
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Default Re: Army Field Telephones and Compatibility?

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Originally Posted by Phil G4SPZ View Post
'I was just interested in confirming that my phones were not faulty, which seems to be the case.'
No, your 'phones aren't faulty.

It might be that there was some sort of signalling protocol established dependent on how they were set up. Many would be linked via a field-exchange using dolls-eye and magneto (hence the 'ring-off' clearing request on the label above the handle).

Perhaps buzzers were used for direct 'phone-phone' calling with strict instructions not to 'Buzz' during conversation? I notice the Soviets didn't fit buzzers to their TAI-43 telephones, and the type Fs were hardly suited to Morse signalling in the same way as the 'D', which actually had a little key rather than a button; I don't really know...
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Old 26th Dec 2009, 1:43 am   #23
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Default Re: Army Field Telephones and Compatibility?

Quote:
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Also, what a/c voltage does the magneto ringer generate e.g. on a Type F?
Generator O/C voltage = 120V RMS.
Generator S/C Current = 96mA RMS.

But typically 78V RMS at 34mA into a 1000R bell-set (measured with Fluke 87V true RMS meter), cranked over at about 17Hz.
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Old 26th Dec 2009, 1:46 am   #24
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Default Re: Army Field Telephones and Compatibility?

Quote:
Originally Posted by GMB View Post
Some clarification required here:

I just found the circuit of a Type D and it shows a buzzer and a bell but no magneto.
It's already been said that a type D has a magneto bell (across L1 and L2 - no series capacitor) but no magneto generator: magneto ringing from field-exchange - one way ringing only?
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Old 26th Dec 2009, 2:09 pm   #25
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Default Re: Army Field Telephones and Compatibility?

Quote:
Originally Posted by russell_w_b View Post
I notice the Soviets didn't fit buzzers to their TAI-43 telephones
My German field telephones don't have buzzers either.

Quote:
the type Fs were hardly suited to Morse signalling in the same way as the 'D', which actually had a little key rather than a button.
Yes, I had wondered whether morse would have been at all practical on a type F, whereas type D's key shouts "morse" at you.
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Old 26th Dec 2009, 2:41 pm   #26
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Default Re: Army Field Telephones and Compatibility?

German FF33 did not have buzzer, I have heard about, but not seen buzzer for their small field exchange. They receive well the buzzer signal.

Swedish Field telephone does have both ringer buzzer and magnetogenerator.

Norwegian field telephones are just magnetotelephones, But we have used a few UK MKII. US, EE8 and german FF33 (captured in wwII)


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Old 26th Dec 2009, 11:13 pm   #27
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Default Re: Army Field Telephones and Compatibility?

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My German field telephones don't have buzzers either.
I'm told that the TAI-43 is a copy of the German 1930s 'Feldspracher' (spelling?), so that would be right. I thought the UK type 'J' might have a buzzer, but no; just a switch to select either Magneto or CB working.
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Old 26th Dec 2009, 11:52 pm   #28
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Default Re: Army Field Telephones and Compatibility?

Could you say how the CB mode works (i.e. what difference is seen on the line)?

I found a circuit and instructons of type J and it seems there is some different way of making and clearing a call in CB mode.

Also, can you have multiple field telephones on the line (when not using a CB exchange)?
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Old 27th Dec 2009, 10:48 am   #29
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Default Re: Army Field Telephones and Compatibility?

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Quote:
Originally Posted by GMB View Post
Also, what a/c voltage does the magneto ringer generate e.g. on a Type F?
Generator O/C voltage = 120V RMS.
Generator S/C Current = 96mA RMS.

But typically 78V RMS at 34mA into a 1000R bell-set (measured with Fluke 87V true RMS meter), cranked over at about 17Hz.
By comparison, a Soviet TAI-43 magneto delivers the following:

Generator O/C Voltage = 189V RMS.
Generator S/C Current = 77.5mA RMS.

Voltage across 1k5 resistor: 79V at 53.3mA.
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Old 27th Dec 2009, 11:54 am   #30
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Default Re: Army Field Telephones and Compatibility?

Quote:
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Could you say how the CB mode works (i.e. what difference is seen on the line)?

I found a circuit and instructons of type J and it seems there is some different way of making and clearing a call in CB mode.

Also, can you have multiple field telephones on the line (when not using a CB exchange)?
Yes, you may have several telephones on the line.

In CB mode the telephone has a capacitor in series to block DC in on hook mode, and in off hook mode something to carry dc, often a coil.
Moast field telephones use batteries even in cb mode.

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Old 27th Dec 2009, 12:01 pm   #31
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Default Re: Army Field Telephones and Compatibility?

Quote:
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Could you say how the CB mode works (i.e. what difference is seen on the line)?
A quick look at the diagram for a 'J' suggests that when the 'CB' switch is pulled, it throws the two 500R bell-coils into parallel and removes the 2u bell-capacitor from cct, and so will allow sufficient DC to make a signalling loop to the exchange. The switch is normally out (capacitor in) when waiting for a call, but, when pulled out, will signal DC to the exchange. It must be replaced after 'hanging up'.

Quote:
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Also, can you have multiple field telephones on the line (when not using a CB exchange)?
Don't see why not - I think I worked out about six would go (type 26A magneto-generator). Bear in mind that the 'J' doesn't have a nice jingly bell; more of a lumpy hammer-action on two bent pieces of metal attached to the case, so using it as a sounding-board!
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Old 27th Dec 2009, 1:46 pm   #32
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Default Re: Army Field Telephones and Compatibility?

I have heard of types D, F, H, J and L.

What other British ones were there or do the letters stand for something?
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Old 27th Dec 2009, 10:02 pm   #33
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Default Re: Army Field Telephones and Compatibility?

Quote:
Originally Posted by russell_w_b View Post

... German 1930s 'Feldspracher' (spelling?)...
I think that's right. My recollections of schoolboy German suggests that Feld means "field" and Spracher (with, more correctly, an umlaut over the 'a') means "speaker", hence Feldsprecher means a field telephone rather than a Fernsprecher ("distance-speaker") which is a normal telephone.

German has a wonderful logic when it comes to making up new words for newly-invented bits of equipment. In the excellent Winter 2009 BVWS Bulletin there is mention of the well-named Farbfernsehgerat (colour distance vision apparatus)...
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Old 28th Dec 2009, 9:00 am   #34
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Default Re: Army Field Telephones and Compatibility?

Feldfernsprecher 33 is buildt up of:

Feld= Field
Fern=far (tele)
sprecher= speaker.
33= modell approved 1933

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Old 28th Dec 2009, 11:07 am   #35
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Default Re: Army Field Telephones and Compatibility?

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'Feldfernsprecher 33'
That's the one!

The Soviets copied it from captured instruments, dubbed 'Hitler-Phones' (but used a 1.5V cell for the mic instead of a 4.5V battery, for some reason...) and the Chinese copied the Soviet version afterwards! (their type 0743 / 0745).
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Old 28th Dec 2009, 6:54 pm   #36
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Default Re: Army Field Telephones and Compatibility?

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'Feldfernsprecher 33'
That's the one!

The Soviets copied it from captured instruments, dubbed 'Hitler-Phones' (but used a 1.5V cell for the mic instead of a 4.5V battery, for some reason...) and the Chinese copied the Soviet version afterwards! (their type 0743 / 0745).
It may be a minor misunderstanding here, my English and German is not that good, but Norwegian forces used the FF33 from about 1950.

Because of politics, and anti-german attitude we used othersr the first years after WWII. Later the fact of having tons of captured FF33's in perfect order made us use this until it was replaced by the Norwegian electronic TP6 from 1970ies. We used some FF33 when I left the service in 1983.

These was orginal, or modified (relabeled and repainted) FF33.

These units had a special 1.5V battery and a low ohm carbon transmitter always marked with a green X.

When putting in transistorized transmitters, the voltage had to be higher.



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Old 29th Dec 2009, 10:19 am   #37
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Default Re: Army Field Telephones and Compatibility?

What's the typical order of magnitude of the voice signal on the line? (and indeed the line impedance for the audio signal)

I was thinking this would be an area of compatibility issues. I notice that they often seem to have a transformer between the local voice circuit and the line.
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Old 29th Dec 2009, 11:51 am   #38
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Default Re: Army Field Telephones and Compatibility?

Quote:
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What's the typical order of magnitude of the voice signal on the line? (and indeed the line impedance for the audio signal)
I measured 8V p-p for a connected type F, with a 4.5V mic battery fitted. Can't say about any others at the moment; my Soviet TAI-43s are at work and I'm not!

Don't get too hung up about line impedances. Think more along the lines of:
  • Single core earth return = two miles.
  • DON10 field-telephone cable, loosely twisted = five - ten miles.
  • Balanced pole-mounted on insulators = ten - twenty miles.

For a rough check, without troubling yourself about characteristic Zo of transmission lines, connect two telephones via a potentiometer and see what resistance you get up to before the speech goes ropey, then equate that to line resistance (typically, fastly and loosely - but from experience, one pair of a multi-pair cable approx. 2/3 mile measures 89 Ohms looped).

Remember 'battle conditions' obviate lots of the niceties one would expect in peace-time, and so maximum flexibility is a bonus.
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Old 29th Dec 2009, 12:19 pm   #39
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Default Re: Army Field Telephones and Compatibility?

Quote:
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Quote:
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What's the typical order of magnitude of the voice signal on the line? (and indeed the line impedance for the audio signal)
'I measured 8V p-p for a connected type F.'
I'd better make clear that this was the p-p voltage measured when I was barking an order like 'gun-fire' or 'ranging salvos'. The maximum level, in other words: 11db up on 0-level into 600 Ohms.
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Old 29th Dec 2009, 11:20 pm   #40
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Default Re: Army Field Telephones and Compatibility?

All measurements and data differs from way of measure, but a telephone shall work between 300 and 3400Hz.
This makes it difficult to hear if you say F or S....

The power from the carbon granulate transmitter equals an amplifier at about 1/1000 watt! (mean value)

The telephone impedance is typical 600 ohms, but may vary from less than 400 to about 900 in real life.

The induction coil acts as a transformer, and is made for matching the transmitter and receiver impedances. You may often have windings for reducing the sidetone.

Other data may be as this:Click image for larger version

Name:	TP_6_.jpg
Views:	77
Size:	62.3 KB
ID:	31378

dsk

Last edited by Dave Moll; 29th Dec 2009 at 11:35 pm. Reason: oversized image converted to thumbnail
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