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Old 21st Feb 2014, 4:26 pm   #1
tovarish cossac
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Exclamation Field telephone help needed.

sSorry if this is the wrong thread to post in, iI'm new to the forum

iI have a TMC type F mkII field telephone with the box. iI have hooked up a 9V battery to it and iI am reading a strong current when the phone would connect to another. aAlso every wire appears to carry a current. tThe phone has both a buzzer and bells.

qQ1: iIs there anyway iI can make the phone make a noise when not connected to another, e.g turning the handle and making the bells ring? aAlso the buzzer button doesn't do anything. tThe plaque on the box says to keep pressed and adjust the bakelite knobs but this didn't do anything.

qQ2: the box has R.SIGNALS stencilled on the front and back, does anyone know if this was stencilled on during the war?

tThanks, cConnor

PS pPlease note that iI have changed the 'makeshift' battery connects that are pictured here.
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Old 21st Feb 2014, 5:33 pm   #2
Dave Moll
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Default Re: Field telephone help needed.

On the set "F", the bells of the calling unit are disconnected while the magneto handle is being turned so that only the remote unit is rung.

As to the buzzer, you should hear sound from the buzzer itself in the local unit if it is adjusted correctly. It is possible to insert the buzzer unit either way round, so please check that it is inserted with the six terminal strips on the left to mate with the springs on the chassis.

Incidentally, the set is designed to run from two 1½V cells, so a 9V battery may not be ideal, especially if you are using a pp3 - for which the current drain may be too great. I would use either "C" or "D" cells in series. A suitable battery holder should fit into the battery compartment intended for the original no. 12 cells.

One further point: if you replace the carbon granule transmitter inset with an electret one, you will need a minimum of 4½V, as 3V just isn't enough to power it. A holder for three "C" cells will likewise fit into the battery compartment.
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Old 21st Feb 2014, 6:44 pm   #3
Phil G4SPZ
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Default Re: Field telephone help needed.

I think the clue to your problem is that "a strong current" is being drawn from the battery. The function of the local battery is to bias the carbon microphone, and that only takes a few milliamps. If the current is much higher, you may have a faulty microphone insert or transformer. Try giving the microphone end of the handset a few sharp taps to shake the carbon granules up a bit. The line terminals are not connected to the battery, but to the transformer secondary winding, so there should be no DC potential on the line.

I agree with Dave that 9 volts is too much. 3 volts may be too little, especially if you have an insensitive earpiece. I use 6 volts on my Tele Fs and it works well.

The best test is to lift the handset and blow into the microphone whilst pressing the hook switch down and releasing it in quick succession. You should hear the rushing sound in the earpiece, interrupted when the hook switch is down. This sidetone is only faint.

As for the "R SIGNALS" legend, I assume this would indicate that this phone originally belonged to the Royal Signals but there's no way of knowing what date it was stencilled on there.
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Old 22nd Feb 2014, 12:51 am   #4
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Default Re: Field telephone help needed.

Tthanks for the quick reply guys. Ii'll get some new batteries Ii know nothing about telephones so sorry if my description was too vague.
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Old 22nd Feb 2014, 9:00 am   #5
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Default Re: Field telephone help needed.

By the way, once you get it working, you really will have to get a second field telephone to get the maximum enjoyment out of it. There's not a great deal you can do with a solitary field telephone.
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Old 22nd Feb 2014, 9:28 pm   #6
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Default Re: Field telephone help needed.

The wiring diagram:
http://img.photobucket.com/albums/v4...e/5ecbb4e4.jpg
says 3V battery. The voltage may be adjusted as suggested over. To high current may cause the granulated carbon in the transmitter capsule to be burnt, and reduce quality of sound considerable. This transmitter may be difficult to replace, and ordinary capsules may be with different characteristic, but will usually work well at 18-50 milli-amps this are often solved by adjusting voltage, but not more than 9 V.
This phone (with batteries) may be used on a regular telephone line, but dont crank it, the equipment in the other end of the line may not resist that. It should ring, and speaking/listening should be OK.
The buzz may also be unhealthy for the telephone system, and the sound my be tough for the listeners ears. As far as I know this phone may work together with any other field telephone in the the world.

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Old 22nd Feb 2014, 10:14 pm   #7
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Default Re: Field telephone help needed.

Quote:
Originally Posted by dagskarlsen View Post
As far as I know this phone may work together with any other field telephone in the the world.
Certainly, I have found that all of my various field telephones can intercommunicate successfully - though only the set "D" and some sets "F" (such as yours) have the buzzer function, the "D" has a bell but no magneto and I have the odd one that does not have a bell (this is another buzzer set).
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Old 22nd Feb 2014, 10:29 pm   #8
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Default Re: Field telephone help needed.

The only problem when using a 'buzzer calling' non-magneto equipped set like the Model D in conjunction with any other type of field telephone is that if the buzzer key is inadvertently pressed during a call, the volume of sound in the distant earpiece is painfully and dangerously loud
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Old 23rd Feb 2014, 9:10 am   #9
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Default Re: Field telephone help needed.

This telephone has both magneto, ringer, buzzer and are together with the Swedish 1936 field telephone with all this implemented as far as my limited experience goes.

Magneto signalling are the most common used, US TA-43 and later need to have the receiver off hook to receive buzzer calls.... but everybody may call and hear your telephone. Some voice powered transmitters may give a very low sound signal in your ear piece but you should still be able to communicate. This is actually not a field telephone, it is a field office telephone.
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Old 24th Feb 2014, 12:43 am   #10
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Default Re: Field telephone help needed.

The Tele F IS a field telephone - we were still using them in the 'field' in the 1960's although in theory they had been replaced by the Tele L and later the Tele J at that time. The buzzer in the Tele F's tended to be replaced with a plug-in induction coil as the 'Switchboard Universal Call 10 Line' (which would receive 'buzzer' calls to operate a relay which latched in to light the calling lamp) was replaced by the 'Switchboard Magneto 10 line'. I didn't see a 10 line UC in use in my service days. Only in 'preservation.

Ian J - lately Lt. Royal Signals in the 1960's
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Old 24th Feb 2014, 8:15 pm   #11
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Default Re: Field telephone help needed.

Quote:
Originally Posted by Pellseinydd View Post
Ian J - lately Lt. Royal Signals in the 1960's
One of my Tele 'F's has been fitted with a rocking armature receiver, very similar to that of a pair of DLR5 headphones, and both my Tele 'J's have been fitted with BA inset receivers. Both types look like 'official' modifications to improve sensitivity, the Tele 'F' normally being fitted with a type 1L receiver (presumably the Tele 'J's would have normally had a receiver 2P in there).

Was this an official MoD mod, as it were?

I suppose the Tele 'F's were not 'battlefield' telephones, requiring, as they did, a flat surface to rest the handset on the cradle switch, whereas the 'D's and 'J's could be hauled about with their PTT switches, and left in any position.
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Old 25th Feb 2014, 1:53 am   #12
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Default Re: Field telephone help needed.

Our issue Tele F's had those balanced armature type - I seem to remember Tele J's having the balanced armature types as well. One of the problems is that once the phones have left their original owners, part get changed - I've seen Tele F's with Tele L handsets !

Last edited by AC/HL; 25th Feb 2014 at 11:19 am. Reason: Unnecessary repeat of the entire previous post removed
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