Barkhausen tubes and other unicomponent oscillators

  1. So in my insatiable curiosity about electron tubes(I've been struggling to find a comprehensive textbook that discusses them-any title suggestions???)I came across the Barkhausen-Kurz Oscillator. So my questions is as follows:

    1. What is the equation(based on applied voltage and current) for the oscillator output frequency?

    2. I presume that this is a sinusoidal oscillator. Are there any electron tube relaxation oscillators that can be driven by a DC input? If not, how would a single component relaxation oscillator tube be constructed?
  2. jcsd
  3. dlgoff

    dlgoff 3,158
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    Welcome to Physics Forums

    This was my "go to" tube reference back in the day.


    For a downloadable pfd file of the 1936 edition go here:
  4. Baluncore

    Baluncore 3,305
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    A Barkhausen tube is not really a single component oscillator. It is an active device that has gain and a self resonance that can be physically tuned to a centre frequency in a specific range. By loading it with a tuned network it can be stabilised and power extracted at the wanted frequency.

    Since the bandwidth of the loading at microwave frequencies is usually insufficient to pass the second harmonic, only the fundamental is available so it will have a sinewave output.

    The relative voltages on the electrodes decide the gain and whether it will oscillate or not. Operating voltages also decide the DC current and the output power available.

    If you are into historical microwave oscillators then I would recommend you get a copy of; Volume 7. KLYSTRONS AND MICROWAVE TRIODES, in “The MIT Radiation Laboratory Series”. Vol 7 is available as a 24 Megabyte pdf download from Jefferson Lab.

    Adjust V7 in the above link for volumes V3 through to V28, the series index.

    Massachusetts Institute Of Technology, Radiation Laboratory Series.
    1. RADAR SYSTEM ENGINEERING — Ridenour (Use )
    3. RADAR BEACONS — Roberts
    4. LORAN — Pierce, McKenzie and Woodward
    5. PULSE GENERATORS — Glasoe and Lebacqz
    7. KLYSTRONS AND MICROWAVE TRIODES — Hamilton, Knipp and Kuper
    8. PRINCIPLES OF MICROWAVE CIRCUITS — Montgomery, Dicke and Purcell
    10. WAVEGUIDE HANDBOOK — Marcuvitz
    14. MICROWAVE DUPLEXERS — Smullin and Montgomery
    15. CRYSTAL RECTIFIERS — Torrey and Whitmer
    16. MICROWAVE MIXERS — Pound
    17. COMPONENTS HANDBOOK — Blackburn
    18. VACUUM TUBE AMPLIFIERS — Valley and Wallman
    19. WAVEFORMS — Chance, Hughes, MacNichol, Sayre and Williams
    20. ELECTRONIC TIME MEASUREMENTS — Chance, Hulsizer, MacNichol and Williams
    21. ELECTRONIC INSTRUMENTS — Greenwood, Holdam and MacRae
    22. CATHODE RAY TUBE DISPLAYS — Soller, Starr and Valley
    23. MICROWAVE RECEIVERS — Van Voorhis
    24. THRESHOLD SIGNALS — Lawson and Uhlenbeck
    25. THEORY OF SERVOMECHANISMS — James, Nichols and Phillips
    26. RADAR SCANNERS AND RADOMES — Cady, Karelitz and Tutner
    28. SERIES INDEX — Linford

    You can usually find a printed copy by searching with the title and first author's name.

    The Information Resources of Jefferson Lab is often worth a visit.
    Last edited: May 12, 2014
  5. jim hardy

    jim hardy 5,460
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  6. Baluncore

    Baluncore 3,305
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    If you want the ultimate vacuum tube application handbook, 1500 pages in 25MByte, google;
    radiotron designer's handbook H4 pdf
  7. dlgoff

    dlgoff 3,158
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    Just downloaded it. Awesome. Is there anything about tubes it doesn't explain?

    BTW Check out page 3 and note the Olathe Kansas Public Library stamp. That's just down the road from one of our mentors and about a 45 minute drive for me. Curious.

    Anyway, thanks. I've got a couple vintage tube products that's on my list to restore. It may come in handy.
  8. jim hardy

    jim hardy 5,460
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    Thanks likewise - old jim

  9. The wikipedia entry on the Barkhausen-Kurz tube describes it as a self-oscillating RF electron tube. Is this not correct? Moreover......What is the response of a Barkausen-Kurz tube to a DC voltage input from experimental data?

    I did see an article from the late 40s or early 50s about a Barkausen oscillator that used an electromagnet to accelerate electrons from the cathode and another electromagnet further down the tube with the opposite polarity to deflect electrons back and create bunched electron clouds.

    Now for a relataxion tube oscillator, I'd imagine it to be some kind of thyratron tube with high plate capactitance.
  10. Baluncore

    Baluncore 3,305
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    By definition, no “component” is ever used “stand alone”. Just as Barkhausen tubes once were, Gunn diodes for example, are used with other circuit components and tuning networks.

    You appear to be looking for a single active component that somehow has the exact frequency and waveform characteristic you want without any external control.

    Why build plate capacitance into the vacuum tube when you can attach it externally and retain the flexibility of design and later adjustment? I do not understand what incentive there can be to to build the frequency determining network inside the glass envelope of the active device.

  11. Good point. What I meant by a unicomponent oscillator wasn't a "standalone" component, but an electron tube which can generate a self-sustaining oscillating output from a DC input where the frequency depends on the input voltage supplied to it. Cavity magnetrons are a good example of the type of component I am talking about. What originally inspired my curiosity is how a self-oscillating electron tube that uses a DC input could be tuned to oscillate at much lower frequency ranges, like audio frequency, and so that is why I need to know how the frequency of a Barkhausen-Kurz tube is determined.
  12. Baluncore

    Baluncore 3,305
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    Unfortunately, cavity magnetron frequency is controlled by the cavity dimensions. Voltage or current operating point, or the magnetic field, have little effect on frequency. The most significant frequency variation of microwave oven magnetrons is from thermal expansion of the structure. They are designed for 2450. MHz and sweep about 100. MHz, that is 4%, in a couple of seconds when power is applied.

    There is no need for vacuum tubes. The CMOS CD4046 chip contains a VCO that would meet your requirements.

  13. Yes, and cavity magnetrons ≠ electron tubes. The thing about tube oscillators is that there are such things as Backwards Wave Oscillators(which are electron tubes with a zigzag wave guide) that can oscillate at frequencies in the terahertz range beyond what semiconductor oscillators are currently capable of. Vacuum tube oscillators, if I recall correctly, have greater frequency stability and tubes in general are less noisy than transistors. I am a firm believer in the supremacy of tubes to semiconductors when it comes to audio electronics and what brought this up is a project I am embarking on to build a vacuum tube synthesizer.
  14. nsaspook

    nsaspook 1,388
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    Vacuum tubes still have their uses in modern equipment but having designed, built and repaired very complex tube devices for 30+ years I can tell you there is nothing 'supreme' about tubes other than they help warm the room when it's cold.

    If you need some audio source ideas for your project do a search for thyratron VCO.
  15. jim hardy

    jim hardy 5,460
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    now there'd be an interesting topic for the general discussion forum, because it's so largely subjective.

    Personal theories are discouraged here on PF, BUT -------

    there are interesting articles from 1980's where scientific measurements were made the harmonic content of tube vs opamp amplifiers driven into distortion,

    and the high output impedance of tube amps vs low output impedance of solid state has to contribute to different transient behavior of the speaker cone(it's a linear motor).

    Yes, it's subjective. A neighborhood Guitar-zan youth once showed me an old Dynaco solid state amplifier which he said "...has an unusual warmth , for a solid state amp". Looking into it i found it took most of its feedback from output current not voltage, so as to mimic a tube amp's high Zout.

    There are articles published in respectable journals. If you find some, maybe mentors would allow such a thread.

    No hijack intended.

    old jim
  16. Baluncore

    Baluncore 3,305
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    I am a firm believer that both tubes and semiconductors have their place when it comes to audio electronics. I am pragmatic and able to make the design decisions needed to select appropriate components to meet the specifications. There is nothing special about a FET with a pilot lamp.

    Magnetrons are vacuum tubes. They support a vacuum, have a filament and a plate current.
    Fleming first invented the vacuum tube rectifier. Lee DeForest added the control grid to make an amplifier.

    As a good example of a tunable vacuum tube oscillator you might consider the gyrotron.
  17. AlephZero

    AlephZero 7,248
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    There are also some interesting psycho-acoustic experiments that showed that people in general actually prefer listening to sound reproduced with a restricted frequency range and added distortion, compared with the undistorted original.

    The experiments used listening tests with music played first by human musicians hidden behind a screen (so the subjects didn't know it was a live performance) who were also recorded, followed by playback of a distorted version of the recording that had just been made.

    The conclusion was that many people preferred the low quality sound that they were familiar with from their own audio equipment, rather than the "real thing".

    I guess this is still true, considering how many people listen to low-bitrate MP3 files played through cheap earbuds!
  18. nsaspook

    nsaspook 1,388
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    I have a fairly good home theater (with acoustic room treatments, etc..) in the house with 8 large speakers of mine that look impressive but are actually vintage Radio-Shack enclosures with new speaker components and crossovers. I've found over the years that a new persons response on how they sound varies with what brand I say they are. I usually start a showing with the lights down so they can't see the equipment and they usually ask sometime during or after the movie. I'm still amazed at how subjective sound quality can be with different expectations. I'm also amazed on how people think electronics can fix a bad rooms sound. In a room designed and build for fine sound a cheap boom-box sounds good.

  19. Nice to hear from someone who has worked with these things! :approve:

    FWIW, a big part of what intrigues me about electron tubes is the ability of certain tubes to self-oscillate when supplied with a DC input voltage. Like the cavity magnetron(@baluncore I stand corrected! Never thought of magnetrons as electron tubes but indeed they are even though the ones I've seen are shaped more like a thick disk), the Barkhausen tube, and the Gyrotron.

    In particularly, I've become interested in Terahertz oscillators to which often use Backward Wave Oscillator tubes. 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?
  20. Baluncore

    Baluncore 3,305
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    Yes and No. That is a truism. By definition, anything “increased to a high enough level” can turn bad.
  21. nsaspook

    nsaspook 1,388
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    We used 'twits' in the electronic warfare and jamming equipment I worked on.

    This is one area where tubes might still be 'supreme'. :devil:
    Even the new gear still uses tubes.

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    Last edited: May 24, 2014
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