Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

"judith" wrote in message
...

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

In the 50's, we used a couple of tin cans connected by string, and that
worked, so an earphone version would have been a luxury ;-)

Down the pub tonight (so it may not all make sense:-)
A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.
So the questions a
would this work?
what would the maximum distance be?

IIRC (and it's a long shot) you used to be able to get galenium
earpieces, and I think they would generate a small electrical current
when "activated" by sound - and would recreate the same sound at the
other end.

Not a clue about the range though :-}

IIRC (and it's a long shot) you used to be able to get galenium
earpieces

A quick google shows "crystal earphone" returning quite a few usable
hits, although fashion seems to have hijacked the "crystal" bit, so
you find daft swarovski tat amongst the results :-}

Alternatively, "piezoelectric earphone"

"judith" wrote in message
...

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

ISTR that carbon granule transducers were used in the very early days,
without power.

"Colin Wilson" o.uk wrote
in message g...
IIRC (and it's a long shot) you used to be able to get galenium
earpieces

A quick google shows "crystal earphone" returning quite a few usable
hits, although fashion seems to have hijacked the "crystal" bit, so
you find daft swarovski tat amongst the results :-}

Alternatively, "piezoelectric earphone"

It certainly doesn't work with 32 ohm electrodynamic earphones - I just
tried it. Although they work quite nicely as a microphone when terminated by
a high impedance (approx 150mV peak output when spoken into in a normal
voice), this figure drops to almost nothing when you load one earpiece with
another of similar impedance. I could see it working ok with crystal
earpieces though, as these will produce upwards of half a volt with a decent
sound level, and a similar high impedance earpiece connected via a length of
cable, should easily respond to produce sound, without unduly loading the
sender earpiece. I would think that the limiting factor as to distance,
given that this is a very high impedance system, will be cable capacitance
rather than resistance, so may actually be rather less than you might
imagine. I would have thought though that you could probably get a couple of
hundred feet ...

Arfa

On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

I seem to remember playing around with army surplus earphones in the early
50s, and seeing articles in comics or maybe even a very old WW or Popular
Electronics or similar suggesting that they could be used as an unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.

"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

I seem to remember playing around with army surplus earphones in the early
50s, and seeing articles in comics or maybe even a very old WW or Popular
Electronics or similar suggesting that they could be used as an unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.

Harry Stottle wrote:
"judith" wrote in message
...

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

In the 50's, we used a couple of tin cans connected by string, and
that worked, so an earphone version would have been a luxury ;-)

We used t'dream of tins cans...



--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

Brass Monkey wrote:
"judith" wrote in message
...
Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

ISTR that carbon granule transducers were used in the very early days,
without power.


I thought they categorically needed a battery. Certainly the
instructions I used to try to do that said so.

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

In article ,
judith writes:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

Yes, it works with a pair of crystal earpieces (which also
work as self-powered microphones). I remember finding this
out somewhere around age 11 when making a crystal radio,
about the same age today's kids start their families.

Distance would probably be limited by cable capacitance,
given the high impedance and low signal level of the crystal
microphone/earpiece, but with something like an old phone
line with two separated bare conductors strung on insulators,
it would probably go a long way.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

I thought they categorically needed a battery. Certainly the
instructions I used to try to do that said so.


Indeed. They're just a variable resistance.

On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

I think that sound powered phones were used during the first world war.
They did however have a hand crank for generating a ringing voltage.

SteveW

"Rod" wrote in message
...
Brass Monkey wrote:
"judith" wrote in message
...
Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

ISTR that carbon granule transducers were used in the very early days,
without power.


I thought they categorically needed a battery. Certainly the instructions
I used to try to do that said so.

--
Rod


The original telephone mouthpieces employed a carbon granule mic. It is a
totally passive device, and works by varying the resistance in a current
path which includes an electrodynamic earpiece at the remote end. It does
this by employing broadly spherical granules of carbon in loose contact with
one another, trapped inside a chamber with conductive side plates at
opposite ends. The diaphragm which collects the sound waves, is physically
connected to one side. The sound vibrations that this picks up, cause the
wall of the chamber to flex minutely in sympathy, which either slightly
compresses the granules, making each one have a greater area of contact with
its immediate neighbours, thereby reducing the resistance path, or the
opposite when it flexes back the other way.

An external current source such as a battery, is then definitely needed to
make use of this varying resistance to produce an electrical signal for
transmission.

Arfa

On Wed, 18 Feb 2009 00:20:58 +0000, judith
wrote:


Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?


These would have been moving Iron headphones - consisting of a pair of
solenoids and an iron diaphragm. The distance they worked over
depended on the connecting cable resistance and the headphone
impedance. I used a pair between my bedroom and a friends house a few
doors away until the neighbours complained about the cables across
thier gardens!

A pair of lodspeakers will produce some sound when used in this way,
but not at a high level.

Harry

In article ,
Brass Monkey wrote:
ISTR that carbon granule transducers were used in the very early days,
without power.

They were the microphone in phones - but the receiver was moving magnet.
And I don't think a carbon granule type actually generates a signal - it
just changes resistance with movement. A moving coil device - like most
headphones - does.

--
*A plateau is a high form of flattery*

Dave Plowman London SW
To e-mail, change noise into sound.

John wrote:
"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?
I seem to remember playing around with army surplus earphones in the early
50s, and seeing articles in comics or maybe even a very old WW or Popular
Electronics or similar suggesting that they could be used as an unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.


I wonder if an electret condenser mic connected via twisted pair to a
standard earphone would work without power..

On Feb 18, 1:20 pm, judith wrote:

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

Yes in 1955 I had a no-battery telephone system in my classroom using
some rather unusual earphones. Perhaps they had a moving magnet and
coils. I didn't try it for more than a few metres.
I removed the dirt from between the floorboards, laid the wire there
and put the dirt back so the wires could not be seen.

On 2009-02-18, John wrote:

"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

I seem to remember playing around with army surplus earphones in the early
50s, and seeing articles in comics or maybe even a very old WW or Popular
Electronics or similar suggesting that they could be used as an unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.



I remember these "surplus" earphones too (sighs and thinks of Lisle
Street and the shop on Church Road, SE19, where I used to drool over HROs and
something with a name like 1155?)

The earphones had ferromagnetic* diaphragms held over a bakelite drum
which had two enamelled copper coils wound around a piece of iron strip,
bent into a U shape. There was a gap of about a millimetre between the
poles of the armature and the diaphragm. The varying current in the
coils would accelerate the diaphragm relative to the armature.

I used mine with a crystal set and later with a superhat radio with
quench control and a mains energised loudspeker that I switched out for
under the bedclothes listening to Radio Luxemburg.

Although irrelevant to their use as earphones, I'd guess that the
armature would have become permanantly magnetised, so that it would act in
reverse as microphone.

You can use modern moving coil headphones as microphones, I've not tried
connecting two pairs together, but if you plug one into a preamplifier
Aux input, it makes a crude pair of microphones. (Earphones, were what
we'd now call headphones. My how those bakelite earcups made your ears
sore after you'd worn them for a few hours!)

What are 'crystal' earphones. Piezoelectric? When did they
become available?

*They were painted black and had a tendency to rust.

Jan Wysocki wrote:
I remember these "surplus" earphones too (sighs and thinks of Lisle
Street

Oh, you mean *those* parts of Lisle Street...


--
Ian White

"Jan Wysocki" wrote in message
k...
On 2009-02-18, John wrote:

"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?


I used mine with a crystal set and later with a superhat radio with

Clearly an early Walkman.....


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

On Wed, 18 Feb 2009 11:15:14 -0000, "Bob Mannix"
wrote:

"Jan Wysocki" wrote in message
. uk...
On 2009-02-18, John wrote:

"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?


I used mine with a crystal set and later with a superhat radio with

Clearly an early Walkman.....

Do I detect the start of a new punthread?


--
Regards, Paul Herber, Sandrila Ltd. http://www.sandrila.co.uk/

In article , "Steve
Walker" wrote:


I think that sound powered phones were used during the first world war.
They did however have a hand crank for generating a ringing voltage.

Do you have this correct? The magneto crank was to generate the ringing
current thereby economising on the use of the battery there to power the
speech circuit. AFAIK sound powered systems used high impedance
headphones, so weren't really telephones - used where the danger of
sparks was to be minimised.

Just Googled: http://www.fairmile.fsbusiness.co.uk/cmk2.htm indicates
there was a battery in that model.
--
John W
To mail me replace the obvious with co.uk twice

On Wed, 18 Feb 2009 01:14:14 -0000, Colin Wilson
o.uk wrote:

Down the pub tonight (so it may not all make sense:-)
A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.
So the questions a
would this work?
what would the maximum distance be?

IIRC (and it's a long shot) you used to be able to get galenium
earpieces, and I think they would generate a small electrical current
when "activated" by sound - and would recreate the same sound at the
other end.

Not a clue about the range though :-}

http://en.wikipedia.org/wiki/Sound-powered_telephone

Old earphones had a magnetic coil and steel or iron disk resonater in
them. Connect two together and speak into one. The vibration of the
metal resonater would create a curent in the coil that was passed to
the other. I don't know what sort of range you could get but a couple
of technicians working alongside me on a ship back in the 70s used one
to communicate with each other when setting up instruments. We just
used radios.

I was quite surprised to see from the wikepedia article they are still
used

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Jan Wysocki
saying something like:

I seem to remember playing around with army surplus earphones in the early
50s, and seeing articles in comics or maybe even a very old WW or Popular
Electronics or similar suggesting that they could be used as an unpowered
intercom. Don't ever remember getting anything to work, though......

Same here. Results were inconclusive, at best.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.



I remember these "surplus" earphones too (sighs and thinks of Lisle
Street and the shop on Church Road, SE19, where I used to drool over HROs and
something with a name like 1155?)

Murphy B40 here - I got one many years later, or rather, the 62B
variant. Still got it - massive towering heap that it is and its
sensitivity is awesome.

On 18 Feb, 00:20, judith wrote:

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

Search for "sound powered telephone". If it was in the '50s he was
quite possibly using mil-surplus, and very likely ex-Naval kit. They
still like sound-powered telephones on-board for damage control, as
they're independent of power sources and Windows for Warships.

The usual way it's done is with moving coil or moving magnet
microphones which will generate a voltage all of their own, so long as
you shout loudly. You can usually spot these as they have a large
"funnel" mouthpiece.

Crystal microphones use a piece of piezo-electric crystal (Rochelle
salt or similar) and will generate enough voltage for a sensitive
earpiece, but hardly enough for a phone.

On Wed, 18 Feb 2009 01:49:47 -0000, "Brass Monkey" wrote:


"judith" wrote in message
.. .

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

ISTR that carbon granule transducers were used in the very early days,
without power.


If I remember correctly, that was the jobbies used in RN ships and
subs, as emergency comms, in case of power failures, easily used over
quite some distances, ie from stem to stern. Worked very well. Not
sure if they they still use them.

On Wed, 18 Feb 2009 12:19:13 -0000, John Weston wrote:

In article , "Steve
Walker" wrote:


I think that sound powered phones were used during the first world war.
They did however have a hand crank for generating a ringing voltage.

Do you have this correct? The magneto crank was to generate the ringing
current thereby economising on the use of the battery there to power the
speech circuit. AFAIK sound powered systems used high impedance
headphones, so weren't really telephones - used where the danger of
sparks was to be minimised.

Just Googled: http://www.fairmile.fsbusiness.co.uk/cmk2.htm indicates
there was a battery in that model.

As far as memory of something read once and a quick search to check my
thoughts. I don't know if they were common, but they seem to have been
used.

SteveW

On Wed, 18 Feb 2009 16:24:07 +0000, Old Git
wrote:

On Wed, 18 Feb 2009 01:49:47 -0000, "Brass Monkey" wrote:


"judith" wrote in message
. ..

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

ISTR that carbon granule transducers were used in the very early days,
without power.


If I remember correctly, that was the jobbies used in RN ships and
subs, as emergency comms, in case of power failures, easily used over
quite some distances, ie from stem to stern. Worked very well. Not
sure if they they still use them.

Think I remembered incorrectly, now believe they were balanced
armature, very effective too. I used to be able to do a fair
impression on the crankwind call noise, which was always a hoot to
watch young sailors running around trying to answer the phone.

In article ,
John Weston wrote:
I think that sound powered phones were used during the first world war.
They did however have a hand crank for generating a ringing voltage.

Do you have this correct? The magneto crank was to generate the ringing
current thereby economising on the use of the battery there to power the
speech circuit. AFAIK sound powered systems used high impedance
headphones, so weren't really telephones - used where the danger of
sparks was to be minimised.

Just Googled: http://www.fairmile.fsbusiness.co.uk/cmk2.htm indicates
there was a battery in that model.

Tele F certainly had a battery - but it lasted so long some might be
excused for thinking it didn't.

--
Is the hardness of the butter proportional to the softness of the bread?*

Dave Plowman London SW
To e-mail, change noise into sound.

"chunkyoldcortina" wrote in message
...
John wrote:
"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?
I seem to remember playing around with army surplus earphones in the
early
50s, and seeing articles in comics or maybe even a very old WW or
Popular
Electronics or similar suggesting that they could be used as an
unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.
I wonder if an electret condenser mic connected via twisted pair to a
standard earphone would work without power..

An electret microphone includes a FET preamp, which is why there is always a
connection back to rail via a resistor (which is actually the FET drain load
resistor) in any equipment which uses one, so the answer is no, it wouldn't
....

Arfa

"Jan Wysocki" wrote in message
k...
On 2009-02-18, John wrote:

"The Wanderer" wrote in message
...
On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

I seem to remember playing around with army surplus earphones in the
early
50s, and seeing articles in comics or maybe even a very old WW or
Popular
Electronics or similar suggesting that they could be used as an
unpowered
intercom. Don't ever remember getting anything to work, though......

--
The Wanderer

Trying to extract useful information from the Internet
is like trying to sip from a firehose.


I did the same - no power. They were moving iron earphones. Clearly the
moving diaphragm created a small voltage.



I remember these "surplus" earphones too (sighs and thinks of Lisle
Street and the shop on Church Road, SE19, where I used to drool over HROs
and
something with a name like 1155?)


That would be the R1155 airborne receiver used by bomber command in WW II.
Its matching transmitter was the T1154

http://www.duxfordradiosociety.org/r...r1155-600p.jpg

Arfa

On Wed, 18 Feb 2009 16:33:09 +0000, Old Git wrote:

snip

Think I remembered incorrectly, now believe they were balanced armature,
very effective too. I used to be able to do a fair impression on the
crankwind call noise, which was always a hoot to watch young sailors
running around trying to answer the phone.


That's it! I was trying to remember what they were called. They had a
corrugated diaphragm, with the armature assembly fastened to the centre
with a tiny nut, didn't they? I used to have a couple of these, from ex-
army field telephones I think.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Wed, 18 Feb 2009 00:20:58 +0000, judith wrote:


A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

would this work?
Yes - as others have said. They were sold as WWII surplus from shops in Lisle
Street and Little Newport street - and by mail order including some cotton
covered wire as a "kit". They were often just two pieces of a headphone with
moving diaphagm.
I have put some pictures up from the pair I bought (apologies for shaky
camera):-
http://www.diy.110mb.com/sound1.jpg
http://www.diy.110mb.com/sound2.jpg
http://www.diy.110mb.com/sound3.jpg
http://www.diy.110mb.com/sound4.jpg

what would the maximum distance be?
Depends on the cable used and how loud you shouted - certainly 100s of yards.

--
Geo

On 18 Feb, 00:20, judith wrote:
Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

Yes, it does. I did it with the speakers/ear-pieces from 1960s
vintage telephones. The speaker had a magnetic diaphragm which was
moved by the current in a solenoid. Talking into it made a miniscule
current that allowed you to be heard at the other end. Pretty carp
really but kept us kids amused for a few minutes.

judith wrote:
Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

It works fine if you use 2 high efficiency transducers of roughly
similar impedance. The classic combination is 2 earpieces from old
telephones. These are balanced armature moving iron transducers. I
expect a pair of crytal earpieces might also work. Modern moving coil
devices are no use, their efficiency is very low, and purely passive
devices such as carbon mics are also no use

You can 'ring' the other party by using a file. Just dont forget by
using these things youre effectively bugging yourself 24/7.


NT

Colin Wilson wrote:
IIRC (and it's a long shot) you used to be able to get galenium
earpieces

A quick google shows "crystal earphone" returning quite a few usable
hits, although fashion seems to have hijacked the "crystal" bit, so
you find daft swarovski tat amongst the results :-}

Alternatively, "piezoelectric earphone"
Yes crystal earpieces worked as mikes (could also get crystal mikes)-
very high impedance 1 M produced volts of signal.
Very useful as you didnt need a high gain amplifier when using them as a
mike and hardly any power when using them as an earpiece.

Used with a diode and a tuning circuit as an "unpowered" radio ie
crystal set.

"judith" wrote in message
...

Down the pub tonight (so it may not all make sense:-)

A colleague said that during the fifties he and his friends used to
make a simple messaging system from a pair of earphones connect
together by a simple twisted pair - no batteries - and that he could
talk to his friends over quire a distance.

So the questions a

would this work?

what would the maximum distance be?

As a kid in 70's I got two old black BT telephone handsets, cut in half,
throw away the mouth peice, expose wires in the solid plastic (bakelite ?),
solder on wire and connect the earpeices back to back. We had a reasonable
communuications system from the den on the climbing frame to den in bushes
at end of garden.

Main issues were wires kept breaking where soldered on and you had to speak
loudly and/or shout to be heard at the other end.

On 19 Feb, 13:09, "Ian_m" wrote:

As a kid in 70's I got two old black BT telephone handsets, cut in half,
throw away the mouth peice, expose wires in the solid plastic (bakelite ?),
solder on wire and connect the earpeices back to back.

Must have been a black one - this doesn't work with the later earpiece
4T that was used in the grey & brown 746 telephones, they're not
sensitive enough as microphones.


Main issues were wires kept breaking where soldered on

Not surprised. If you mean the handset cord, that stuff was a tinsel
conductor and effectively unsolderable. I'm surprised it worked at all
- whenever I did the same thing as a kid I always had to use screw
terminals.

In article ,
Ian_m wrote:
As a kid in 70's I got two old black BT telephone handsets, cut in half,
throw away the mouth peice, expose wires in the solid plastic (bakelite
?), solder on wire and connect the earpeices back to back. We had a
reasonable communuications system from the den on the climbing frame to
den in bushes at end of garden.

Main issues were wires kept breaking where soldered on and you had to
speak loudly and/or shout to be heard at the other end.

If you've got complete telephones all you need is a battery in one to link
them. It can be switched off by the receiver rest too. And will last for
ever.

--
*Growing old is inevitable, growing up is optional

Dave Plowman London SW
To e-mail, change noise into sound.