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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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15th Jul 2010, 4:29 pm | #1 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
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Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
I'm knocking up a simple circuit to demonstrate to my young nephew a basic 'telephone', i.e: Type 16 Carbon Transmitter, wired with twin bell wire to a 4T Receiver, using a 1.5V battery in one line.
Does it matter which way the battery goes round, as it seems to work either way round ?
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15th Jul 2010, 5:24 pm | #2 |
Octode
Join Date: Aug 2006
Location: Rye, East Sussex, UK.
Posts: 1,647
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
... that depends on whether you want the 'bringg' or the 'bringgggg' first!
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15th Jul 2010, 5:47 pm | #3 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
As a carbon transmitter is merely a resistance which varies according to the variable air pressure caused by the speech, it will work either way round. What the receiver is responding to is the variations in the voltage thus caused and again will work either way round. Be aware, however, that this arrangement will result in a DC voltage across the receiver, but at 1.5V, I wouldn't have thought this likely to cause any damage. Those with more in-depth knowledge of telephone circuitry may be able to give definitive advice on this.
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15th Jul 2010, 6:27 pm | #4 |
Dekatron
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Location: Lynton, N. Devon, UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
I'd suggest that the polarity is going to be slightly more important to the receiver than to the carbon microphone - whether the standing DC augments or diminishes the permanent magnet. Either will work, and I'm almost sure that telephone receivers are tolerant of this - but it used to be 'good practice' with headphones to connect so that the diaphragm is pulled slightly inwards, so that the standing DC doesn't have a demagnetising effect oin the magnet.
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15th Jul 2010, 9:16 pm | #5 | |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
Quote:
If you have an old relay or choke and a suitable capacitor, you could route your DC to the mic via the relay (choke) and connect your receiver, with the capacitor in one leg, across the wires that go to your carbon mic, thus forming a rudimentary 'transmission bridge', so that the AC speech goes via the capacitor to the receiver and the relay (or choke) prevents the speech from going around the battery. The DC will be blocked from the receiver, but will energise the carbon mic.
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16th Jul 2010, 11:28 am | #6 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
Many thanks everyone for the replies & info. This set-up is only for demo and not for long-term or continuous use.
I'm 'ejakating' him in sound transmission, started with 2 tins and string, then 2 GPO type 4T's & bell wire and now the carbon transmitter, battery & a 4T. The next amazing trick will be transmitting sound on a light beam....he thinks I'm a magician!
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |
16th Jul 2010, 11:32 am | #7 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
Just to add, I'm trying to catch him early so that he'll be become an obsessed collector like me.
I remember my Physics teacher at school who demostrated such 'magic' when I was about 11 and from then onwards I was hooked!
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |
16th Jul 2010, 1:42 pm | #8 | ||
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
Quote:
Quote:
I remember an article in 'Pratical Electronics' from years ago, modulating a sealed-beam car-headlamp (I think it was) at one end and using a focussed LDR at the other. Something like that, but with LEDs instead?
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16th Jul 2010, 1:55 pm | #9 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
When I worked at Chubb Alarms, they produced a valve operated 200ft beam system (walk between transmitter & receiver and the alarm was triggered). It wasn't IR but used a value detector and a focused light bulb.
One of the techie lads set up one on the outside of the factory wall and modulated it to transmit/receive sound. We used it to talk to the repairs dept at the other end of the factory. One day we were playing with it and chatting with one of the guys in the repairs dept and we could hear a strange "plinking/plonking' interference on the sound....it turned out that it was raining outside and causing the noise.
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |
16th Jul 2010, 2:03 pm | #10 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
T'other day I had my nephew puzzled by placing an 8" Base Speaker on the table (with another hidden one wired to it under the table)
Then, I placed a handfull of rice on the cone of the visible speaker and amazed him with bouncing rice (whilst tapping on the cone of the hidden speaker) ! That's when he told me that I was the best uncle in the world!..... (Bless)
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! Last edited by camtechman; 16th Jul 2010 at 2:04 pm. Reason: spelling error |
18th Jul 2010, 11:26 pm | #11 |
Dekatron
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Location: Leominster, Herefordshire, UK.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
I remember building a version of the sliding shutter modulator for this out of a deconed old loudspeaker, some aluminium strip and a cornflakes packet while I was at college. It beat the pants off just directly modulating a torch bulb by connecting a bulb and battery in series via the loudspeaker secondary of a valve amplifier!
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19th Jul 2010, 1:23 am | #12 | |
Heptode
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Location: Indianapolis, Indiana, USA.
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
Quote:
http://www.qtl.co.il/img/copy.pnghttp://www.google.com/favicon.icohttp://www.qtl.co.il/img/trans.png
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Just playing with high voltage.... |
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22nd Jul 2010, 7:30 pm | #13 |
Nonode
Join Date: Jan 2008
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Re: Polarity Of Battery In Simple Carbon Transmitter To Type 4T Receiver?
LOL!
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |