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Old 4th November 2012, 11:28 PM   #1
Pano is offline Pano  United States
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Question Amplifiers in 1836?

Was the (electrical) amplifier invented at the Smithsonian Institute in 1836?

We generally credit the triode with the beginning of amplification, making long distance voice communications possible. But what about long distance telegraphy? What did they do to boost weak signals?

They used relays. An electromagnetic switch (relay) can be made to operate with very little current switching heavier current flows to do more work, such as make a sound or ring a bell. That's what was often used on long telegraph lines when the current was weak. Very clever! (remember, this was the 1830s). A weak signal could automatically be turned into a stronger one.

In his 1860 book "History, Theory, and Practice of the Electrical Telegraph" George Prescott says:
Quote:
The effect of the combination of circuits is to enable a weak or exhausted current to bring into action and substitute for itself a fresh and powerful one. This is an essential condition to obtaining useful mechanical results from electricity itself, where a long circuit of conductors is used, and accordingly it received the attention of early experimenters with the telegraph. This principle seems to have been first successfully applied by Professor Joseph Henry, of the Smithsonian Institution, in the latter part of 1836. He was thus enabled to ring large bells at a distance, by means of a combined telegraphic and local circuit.
The "local circuit" is the high current side supplied thru a local battery and controlled by the relay.

In those days they could amplify electrical pulses, and they didn't need no stinkin' vacuum tubes or transistors. It might have been slow and it might have been digital (dot or dash) by it was electrical amplification.
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Old 5th November 2012, 02:06 PM   #2
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Sounds to me that they "invented" the class D amp, they just had a very slow and jittery clock.
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Old 5th November 2012, 03:57 PM   #3
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If you count a relay as amplification, then you might have to consider sending a runner to throw a big switch as amplification too!
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Old 5th November 2012, 05:34 PM   #4
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Hi,

Its not "linear amplification". It is a pulse (re)transmission system.

rgds, sreten.
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Old 5th November 2012, 08:06 PM   #5
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Yes, non-linear amplification.

DF96. I see your point, but where does one draw the line? There is mechanical amplification and electrical. I guess I would call amplification the control of a strong signal by a weaker one, whatever that signal might be. A person flipping a switch could qualify as a small force controlling a lager one, for sure, but it's hardly automatic. Having the device do it, instead of you or your servant, is what makes it "amplification" for me.
"The process of increasing the magnitude of a variable quantity, especially the magnitude of voltage, power, or current, without altering any other quality." Is a typical definition.


Certainly a relay isn't linear amplification, but it does allow a small signal to control a larger one without human intervention. Does amplification have to be linear (or nearly) to qualify? Does a relay count as an amplifier? Or is it just pulse retransmission?

The long lines between Nova-Scotia and Ireland are what led us to transmission line theory, of course. Tho it was more the second and third cables of the 1860s than the first, ill fated cable of 1858. The telegraph taught us a lot about electricity.
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Old 5th November 2012, 09:04 PM   #6
DF96 is offline DF96  England
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I think I would expect an amplifier to have an output which bears some relationship with the strength of the input. Not necessarily purely linear, but some element of linearity.
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Old 5th November 2012, 09:21 PM   #7
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Quote:
Originally Posted by Pano View Post
"The process of increasing the magnitude of a variable quantity, especially the
magnitude of voltage, power, or current, without altering any other quality."
Is a typical definition.
Hi,

Except the variable has no magnitude quality, its on/off in the time domain.
Maintaining the transmission of that state is not linear amplification, though
its also true to say the transmission path does amplify the pulse at points,
via relays, but they don't change the nature of the information passed.

rgds, sreten.

Fair to say digital transmission preceded analogue.

FWIW there were some pretty wacky relatively short distance mechanical
systems developed, e.g. using air pressure with "repeater stations" similar
to the use of relays, mainly in cities to do with clock synchronisation.
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Last edited by sreten; 5th November 2012 at 09:35 PM.
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Old 5th November 2012, 09:54 PM   #8
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Quote:
Originally Posted by DF96 View Post
I think I would expect an amplifier to have an output which bears some relationship with the strength of the input.
The relay system did, but loosely. There had to be some change in signal strength to make the relay work (on, off, on). Too weak and it would not work at all. Too much current also seems to have been a problem.

The reason I see it as an amplifier may be because of our modern view of them. When the signal on the line was too weak to activate the "sounder", they used the relay to detect the weak signal and switch a stronger, local current that could swing the electromagnets in the sounder. Making a weak signal audible.

They also used Kelvin's mirror galvanometer for very weak currents, such as on the trans-Atlantic line. That I would call measurement or display, not amplification because the weak signal actually moved the mirror.

Anyway, it's interesting to read and think about the circuit problems faced by the telecommunication geeks of 160 years ago. So much of it was new territory.
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