When was the first Signal Amplifier invented? Was it because of the Telegraph?

I studied amplifiers in school. The old ones, push pull with dual tubes like the 6L6. I can’t recall who is credited with inventing the first signal amplifier.

When were Amplifiers first invented? Did they have to wait for the invention of the vacuum tube?

How did the early telegraphs boost their signal across the country? Did they have primitive amplifiers? Maybe they used a step up transformer? I’ve wondered how electronics got off the ground without amplifier circuits? Sort of a chicken/egg deal.

The first signal amplifiers used vacuum tubes and were used to amplify telephone (not telegraph) signals. The use of vacuum tube amplifiers significantly increased the capability of telephone systems at the time and allowed the first coast to coast telephone systems to be constructed.

Telegraph used direct current. You could extend the signal range by using simple electromechanical relays.

Vacuum tube amplifiers weren’t invented in a single step. Research by folks like Frederick Guthrie, Thomas Edison, John Ambrose Fleming, and Lee De Forest all contributed through the late 1800s and early 1900s to create the first practical amplifiers.

It is worth mentioning that amplification is not specific to electrical systems, with pneumatic and hydraulic amplifiers being important ideas too.

In the annals of telecommunication there is a curious device - the coherer that sits in the grey zone. An amalgam of detector and amplification. It won’t amplify in the sense that a given input is reproduced at a greater level, but its ability to produce useful levels of DC in response to weak RF energy made it quite important in early communications.

OK, let’s go for the gusto, and expand on what Francis Vaughan said: The ‘fluidistor’ is to fluids what the transistor is to electrical current. That article is a little optimistic about how useful they’d be*, but they are useful and there are somehwat more modern patents related to them. Coming (almost) full-circle, we have nanoscale fluidistors that use electricity to control the flow of ions.

*(It’s an article from 1960 predicting that fluidistors might challenge electronics for supremacy in computing devices in ten years.)

All of this falls under the heading of fluidics.

Thank you. :wink:

I’d wondered about this for a long time. Especially the early telegraphs and how they got a signal cross country. This was at least 60 years before commonly vacuum tubes were commonly available.


when electromechanical relays were used to extend the telegraph they were called repeaters. repeater is still used as a term for electronic amplifiers in that type of function.

IMO, it was not the invention of electronic amplification that is most fascinating. It was the introduction of negative feedback to amplifiers.

Negative feedback was revolutionary, and it was invented by Harold Black:


(Of course, if he had not invented it, someone else would have. But it’s still a great story.)

Don’t forget that musical instruments are signal amplifiers as are some buildings.

To add to this, the early telegraphs didn’t make dot-and-dash tones like the audio Morse code we are used to hearing today. Because there were merely electromagnets being controlled from a long distance away, the receivers were levers that made mechanical clicking noises as they jerked up and down. Two clicks – an up and and down – close together was a dot, and a longer space between the two clicks was one of the dashes. This simple design made it possible to easily connect one line, with a weak current, into a repeater for the next line, controlled by the signal from the original line, but sending out its signal using a fresh battery.

in 1835 Joseph Henry invented the critical electrical relay, by which a weak current could operate a powerful local electromagnet over very long distances.

I seem to remember seeing giant structures designed to amplify sound of aircraft before radar was invented, surely those should count.

Do you mean these?

A common modern engineering take on amplification tends to only consider active devices as amplifiers. Using an input of some form to control a more potent source of energy. The big sound collecting horns, and other concentrating devices are not active - but passive. This is at variance with the proper meaning of the word, but very common.

Prior to vacuum tubes there were a couple of options for electrical amplification.

It is possible to use a telephone receiver (speaker) to drive a telephone transmitter (carbon microphone) and achieve net gain. The two were integrated into a single unit sharing a common diaphram when this was done.

An amplidyne is a brushed DC generator with the field current controlled by the signal to be amplified. In later years this was provided by vacuum tube output, but the early ones drove the field directly from a carbon mic. The iconic trucks with the speakers on top typically had an amplidyne belted to the engine driving those speakers. Specially constructed amplidynes were even able to operate as long wave radio transmitters.

:slight_smile: I had heard stories about structures to amplify sound. This is the first time I’ve seen a photo of them. Thank you for sharing.

There’s some very interesting technology linked in this thread. A lot of it I’d never heard of before.

Although they were made redundant by radar it wasn’t a complete waste of money. A command and control network had been established to make use of the information gleaned from these devices. When radar did come along, that network was easily adapted to serve the needs of the new technology.

And to repeat what was said above, those are *not *amplifiers. They may have concentrated the incoming sound and therefore made it audible to humans, but they weren’t amplifiers.

The difference is active vs passive. Is some external source of power being controlled by the input signal to create a new signal which is the same shape as the input signal but bigger? If not, it’s not an amplifier.

Vacuum tube amplifiers were important not just for communications, but because they enabled reliable scientific measurement of small signals. Prior to this, if you wanted to take a spectrum, for instance, you took a photograph, then analyzed the strength of the lines on the photograpoh. With amplifiers, you could put a detector at the focus of your spectrometer and amplify its output and send it to a chart recorder. Chart recorders, in fact, started coming out after the invention of the vacuum tube.

Vacuum tube amplifiers were also the key to sound films. There were “talkies” long before The Jazz Singer. The Edison-Dickson sound film was made in 1894-5, and as a pretty obvious dodge for people who were instrumental in making both motion pictures and phonographs.

Dickson even made kinetoscopes with earphones and phonograph records in them, but it wasn’t a big success (no synchronization, for one thing). There were lots of schemes for putting sound directly on the film through the 19-teens and into the 1920s. But none of it meant anything if you couldn’t get the sound out to a full auditorium of people. Amplifiers using vacuum tubes let them do that, and gave us sound movies.

The whole point of Morse’s invention, (as he saw it, anyway) was that it provided a written record of the message (on the tape that clerks are always reading in Western movies). When he learned that the clerks were reading the messages by listening to the clicks of the tape printer he ordered that anyone detected so doing should be instantly dismissed.

When were magnetic amplifiers invented? I have never seen one…are they still in use?