# Barkhausen tubes and other unicomponent oscillators

by EinsteinKreuz
Tags: barkhausen, oscillators, tubes, unicomponent
Thanks
P: 1,957
 Quote by EinsteinKreuz Now in the case of transistors for audio devices like amplifiers, isn't there an issue of base-emitter breakdown(leading to unwanted noise) when the amplifier power is increased to a high enough level?
Yes and No. That is a truism. By definition, anything “increased to a high enough level” can turn bad.
P: 663
 Quote by EinsteinKreuz In particularly, I've become interested in Terahertz oscillators to which often use Backward Wave Oscillator tubes.
We used 'twits' in the electronic warfare and jamming equipment I worked on.
http://en.wikipedia.org/wiki/AN/SLQ-..._Warfare_Suite

This is one area where tubes might still be 'supreme'.
Even the new gear still uses tubes.
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PF Gold
P: 2,734
 Quote by nsaspook We used 'twits' in the electronic warfare and jamming equipment I worked on.
Damn. You really are a spook. Awesome.
P: 663
 Quote by dlgoff Damn. You really are a spook. Awesome.
I was just another grunt keeping things running but I was one of those guys who could fix anything. It was a nice toy but we all knew if the crap hit the fan the Russians would just launch everything they had at once to wipe us off the planet and we had a very short lead time to do the same thing.
The TWT type tubes are unique in their ability to generate high power across a wide band of radar frequencies and when designed as a LNA, provide a very low noise amplification front-end for receivers that made them perfect for a wide-band radar detector that's also resistant to EMP. They are still being used in communication satellite transponders today.

http://www.r-type.org/articles/art-030.htm
http://www3.alcatel-lucent.com/bstj/...j42-4-1703.pdf
PF Gold
P: 2,734
 Quote by nsaspook They are still being used in communication satellite transponders today.
Just because you're an "old spook" doesn't take away from you being awesome.
 P: 10 As it turns out, Vacuum tubes are making a comeback at a much tinier scale. But technical books about them are extremely scarce and usually >50 years old(out-of-print)! I have found a plethora of books on amazon dot com about audio frequency vacuum tube amplifiers, but pretty much nothin about vacuum tube oscillators(audio frequency OR radio frequency)which is frustrating since the latter are what interest me.
 Sci Advisor Thanks P: 1,957 From 20Hz to 20kHz is a factor of 1000, so audio amplifiers need to have a very wide flat response. Oscilloscope vertical deflection amplifiers and radar receivers also required wide bandwidth. In about 1897, Sir Oliver Lodge in London invented radio frequency tuning. Vacuum tubes followed soon after, so RF amplifiers and oscillators using VTs are usually relatively narrow band circuits with high Q. They often employ deliberate narrow band selectivity. Since WW2 we have gradually migrated to spread spectrum and digital, both of which require wide bandwidth. But we do not use VTs since semiconductors are more reliable and use less power for signal processing. There is plenty of VT narrow band amplifier and oscillator theory out there. Begin with the older ARRL or RSGB handbooks. Download the RMIT Rad Lab books from my earlier link if you want theory. Vol 18, Vacuum Tube Amplifiers. Vol 28, Series Index, has 3 pages indexing VT oscillators of all sorts from audio through to microwave.
 Sci Advisor Thanks P: 1,957 Understanding the interaction of phase, gain and feedback are very important in amplifier design. Since VT amplification became available, many aspiring amplifier designers have failed in an attempt to design a stable wide-band, high-gain amplifier. Some, such as; Barkhausen-Kurz, Butler, Clapp, Colpitts, Cutton-Touly, Franklin, Gill-Morell, Hartley, Mesny, Pierce, Robert Dollar, Squire, and Vacker, have turned failure into success by giving their names to oscillators.
P: 663
 Quote by EinsteinKreuz As it turns out, Vacuum tubes are making a comeback at a much tinier scale. But technical books about them are extremely scarce and usually >50 years old(out-of-print)!
Go to archive.org: https://archive.org/search.php?query=vacuum%20tubes
P: 10
 Quote by Baluncore From 20Hz to 20kHz is a factor of 1000, so audio amplifiers need to have a very wide flat response. Oscilloscope vertical deflection amplifiers and radar receivers also required wide bandwidth. In about 1897, Sir Oliver Lodge in London invented radio frequency tuning. Vacuum tubes followed soon after, so RF amplifiers and oscillators using VTs are usually relatively narrow band circuits with high Q. They often employ deliberate narrow band selectivity. Since WW2 we have gradually migrated to spread spectrum and digital, both of which require wide bandwidth. But we do not use VTs since semiconductors are more reliable and use less power for signal processing. There is plenty of VT narrow band amplifier and oscillator theory out there. Begin with the older ARRL or RSGB handbooks. Download the RMIT Rad Lab books from my earlier link if you want theory. Vol 18, Vacuum Tube Amplifiers. Vol 28, Series Index, has 3 pages indexing VT oscillators of all sorts from audio through to microwave.

Will do(downloads). But what about Backward Wave Oscillators? Semiconductors have hit the lower limit for size and are almost to the upper limit for oscillator frequency. I know of no physical reason why electron tube backward wave oscillators couldn't be designed to oscillate at frequencies with multiples of 10 to 100 Thz.....beyond. Did you see the link I posted about microscopic vacuum tubes?
P: 663
 Quote by EinsteinKreuz Semiconductors have hit the lower limit for size and are almost to the upper limit for oscillator frequency.
There are semiconductor designs that extend the range into the thz range with quantum mechanical effects.

http://en.wikipedia.org/wiki/Resonant-tunneling_diode
 Sci Advisor Thanks P: 1,957 @EinsteinKreuz. A research news item constitutes a dream, not a movement. I still work with VTs in the real world and I do not have your rosy view. I put my effort into removing relays, monostables and VTs rather than looking for opportunities where I might bring them back. Making free running oscillators is not the problem, we now need to generate and receive modulated data streams. Optical data links employ semiconductor transducers, so they really can not need VTs. VTs will never match a FET semiconductor on speed, or noise figure at room temperature. How might you cool a VT amplifier to 5°K. There are situations where VTs are still the answer. There are also situations where a VT has no application. For example, there are “non-linear transmission lines” made from semiconductors that sharpen pulse edges and make data links, sampling mixers and oscilloscopes with quite ridiculous speed and resolution. That cannot possibly be done with VTs.
 P: 663 In the end it's tubes that get the last laugh. Every transistors daddy is a tube, it might be a big tube with lots of vacuum pumps and controllers but most of the machines that form the basic layers and do the doping have the basics of filaments, cathodes, control grids, suppression grids or plates and anodes in their guts.
P: 10
 Quote by Baluncore @EinsteinKreuz. A research news item constitutes a dream, not a movement. I still work with VTs in the real world and I do not have your rosy view. I put my effort into removing relays, monostables and VTs rather than looking for opportunities where I might bring them back. Making free running oscillators is not the problem, we now need to generate and receive modulated data streams. Optical data links employ semiconductor transducers, so they really can not need VTs. VTs will never match a FET semiconductor on speed, or noise figure at room temperature. How might you cool a VT amplifier to 5°K. There are situations where VTs are still the answer. There are also situations where a VT has no application. For example, there are “non-linear transmission lines” made from semiconductors that sharpen pulse edges and make data links, sampling mixers and oscilloscopes with quite ridiculous speed and resolution. That cannot possibly be done with VTs.

Well yes. These microscopic vacuum tubes are still in the R&D phase and haven't fully been put into use. And I do not dispute that there are electronics applications where VTs aren't useful and can only be done with semiconductors. And do not misunderstand me: I was not saying that semiconductors are useless!
P: 10
 Quote by nsaspook There are semiconductor designs that extend the range into the thz range with quantum mechanical effects. http://en.wikipedia.org/wiki/Resonant-tunneling_diode

True. But the thing is that electrons in semiconductors have certain allowed energy states(energy bands)whereas free electrons can have any energy. The higher the oscillation frequency of an electron or a photon the higher the energy it carries( E = h$\nu$)so if you want to go up to frequencies that are in the 100 Thz or Petahertz range and beyond it would be easier to accomplish this with free electron tubes. There is a team of scientists in Deutschland developing an opto-electronic petahertz oscillator using femtosecond laser pulses.

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