simple transmitter - receiver

[Bob Mannix]

Clearly an early Walkman.....

[Paul Herber]

Do I detect the start of a new punthread?

[John Weston]

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:

indicates there was a battery in that model.

[Alang]

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

[Grimly Curmudgeon]

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:

Same here. Results were inconclusive, at best.

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.

[Owain]

Wikipedia suggests balanced armature, which is what would probably have been used in headphones in the 50s.

[Andy Dingley]

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.

[Old Git]

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.

[Steve Walker]

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

[Old Git]

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.

[Dave Plowman (News)]

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

[Arfa Daily]

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

[Arfa Daily]

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

[mick]

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.

[Geo]

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):-

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

[Onetap]

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.

[meow2222]

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

[robert]

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.

[Ian_m]

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.

[Andy Dingley]

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.

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.