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Magnetic amplifiers existed before triodes, dating back to at least 1885: https://en.wikipedia.org/wiki/Magnetic_amplifier https://en.wikipedia.org/wiki/Magnet

by mrob 3y ago

Magnetic amplifiers existed before triodes, dating back to at least 1885: https://en.wikipedia.org/wiki/Magnetic_amplifier https://en.wikipedia.org/wiki/Magnetic_amplifier However, these have the major drawback that they can only control the amplitude of an AC signal, and that with a lot of distortion. They could only be used to amplify audio with reasonable quality by amplitude modulation of a sufficiently high-frequency carrier, which itself was difficult to generate before vacuum tube amplifiers. As far as I know, the only two techniques that could do it were excitation of an LC resonant circuit using a carbon arc lamp, or using a very fast alternator that worked a lot like the Teleharmonium itself. See: https://en.wikipedia.org/wiki/Arc_converter https://en.wikipedia.org/wiki/Arc_converter https://en.wikipedia.org/wiki/Alexanderson_alternator https://en.wikipedia.org/wiki/Alexanderson_alternator The AM signal could then be demodulated using various techniques that existed before the triode, e.g. a vacuum tube diode (invented before the triode in 1904), or if you don't want to use vacuum tubes at all, a crystal detector (principle discovered in 1874) or electrolytic detector (invented 1903), although I'm not sure those have the power handling capability to be useful for what the Teleharmonium was doing.

Animats 3y ago
Magnetic audio amplifiers can be built. Here's a small hobbyist one.[1] You need a 35Khz power supply, which is no big deal today, but a problem in 1885. Alexanderson alternators could do it. Those things were huge because they wanted tens or hundreds of kilowatts out. The last one still working was rated for 200KW.[2] If you only need 50W or so, it could be much smaller. This would be a cool hobbyist project today. Run a motor at 30,000 RPM (Dremel tools can do this), and have an 80-pole generator, which is just a slotted disk surrounded by windings, to get 40KHz. That's an Alexanderson alternator in mini size. Once there's power, the magnetic amplifier stage can work.[1] Low-power audio comes in, and higher power audio comes out. Need a low-pass filter at the end. Getting the distortion down is probably going to be the hard part. The keyboard end of things would use tone wheels, like a Hammond organ. Not as big as the ones in the Teleharmonium, though, because you're not generating high power audio that way. A magnetic preamplifier could be used to get those signals up to a useful level. The Teleharmonium was built when insulated wire was hard to get. Inventors had to build their own parts. There were no instruments such as oscilloscopes to look at high-frequency waveforms. Early electronics involved a lot of wondering what was going on in there. Today, you can look at the waveforms and see what's going wrong. So, not too bad to build today. Not useful, but might be fun. I miss the TechShop days. [1] http://sparkbangbuzz.com/mag-audio-amp/mag-audio-amp.htm http://sparkbangbuzz.com/mag-audio-amp/mag-audio-amp.htm [2] https://alexander.n.se/en/the-radio-station-saq-grimeton/the-alexanderson-transmitter/ https://alexander.n.se/en/the-radio-station-saq-grimeton/the...
tlb 3y ago
Another approach was basically a speaker connected to a carbon microphone, which compressed loosely packed carbon granules to change its resistance. They were used as repeaters in long distance telephone lines as early as 1904: https://en.wikipedia.org/wiki/Carbon_microphone#Use_as_amplifier https://en.wikipedia.org/wiki/Carbon_microphone#Use_as_ampli...

by mrob 3y ago

Animats 3y ago

Magnetic audio amplifiers can be built. Here's a small hobbyist one.[1] You need a 35Khz power supply, which is no big deal today, but a problem in 1885. Alexanderson alternators could do it. Those things were huge because they wanted tens or hundreds of kilowatts out. The last one still working was rated for 200KW.[2] If you only need 50W or so, it could be much smaller. This would be a cool hobbyist project today. Run a motor at 30,000 RPM (Dremel tools can do this), and have an 80-pole generator, which is just a slotted disk surrounded by windings, to get 40KHz. That's an Alexanderson alternator in mini size. Once there's power, the magnetic amplifier stage can work.[1] Low-power audio comes in, and higher power audio comes out. Need a low-pass filter at the end. Getting the distortion down is probably going to be the hard part. The keyboard end of things would use tone wheels, like a Hammond organ. Not as big as the ones in the Teleharmonium, though, because you're not generating high power audio that way. A magnetic preamplifier could be used to get those signals up to a useful level. The Teleharmonium was built when insulated wire was hard to get. Inventors had to build their own parts. There were no instruments such as oscilloscopes to look at high-frequency waveforms. Early electronics involved a lot of wondering what was going on in there. Today, you can look at the waveforms and see what's going wrong. So, not too bad to build today. Not useful, but might be fun. I miss the TechShop days. [1] http://sparkbangbuzz.com/mag-audio-amp/mag-audio-amp.htm http://sparkbangbuzz.com/mag-audio-amp/mag-audio-amp.htm [2] https://alexander.n.se/en/the-radio-station-saq-grimeton/the-alexanderson-transmitter/ https://alexander.n.se/en/the-radio-station-saq-grimeton/the...

tlb 3y ago

Another approach was basically a speaker connected to a carbon microphone, which compressed loosely packed carbon granules to change its resistance. They were used as repeaters in long distance telephone lines as early as 1904: https://en.wikipedia.org/wiki/Carbon_microphone#Use_as_amplifier https://en.wikipedia.org/wiki/Carbon_microphone#Use_as_ampli...