Yes, useful thyratron relaxation oscillators exist

Discussion in 'Feedback and Suggestions' started by atomota, Jan 28, 2008.

  1. atomota

    Thread Starter New Member

    Jan 28, 2008
    2
    0
    I was reading the Gas Discharge Tube page http://www.allaboutcircuits.com/vol_3/chpt_7/2.html where it says:
    About ten or twelve years ago, tube guru Eric Barbour made a synthesizer VCO using a 2D21 thyratron. Variants of this oscillator appear in his commercial MIDI-controlled Phattytron (http://www.keyboardmuseum.com/ar/m/meta/pt1.html) and in his TM-3 Gas-Tube Dual VCO with Suboctave, available to this day from Metasonix (http://www.metasonix.com/index.php?option=com_content&task=view&id=14&Itemid=31).

    I breadboarded up one of these oscillators long ago. It stayed in tune and sounded cool. Frequency control and sine waves aren't everything.

    Analog music synthesizers have been using relaxation oscillator VCOs built with solid-state components since at least the 1960s. The frequency control is excellent, and the resulting sawtooth wave sounds nice, is rich in harmonics, and serves as the basis for deriving other standard musical waves (square, pulse, triangle, sine).
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Thanks for the supplementary information. The e-book entry should be updated to acknowledge that a VCO has been practically implemented by both Eric Barbour and yourself.

    Feel free to share with us your endeavours with his project.

    Dave
     
  3. atomota

    Thread Starter New Member

    Jan 28, 2008
    2
    0
    My endeavors, yes . . . I wanted to try to get a more traditional sawtooth out of the oscillator, so I tried a more traditional synth oscillator architecture. A 12ax7 was used as a voltage-controlled constant current source to charge the capacitor to get a linear ramp. Looking back, I can't figure how I must have had the thyratron connected; it's probably in an old notebook. It worked but the tuning range was not large enough to be useful. Then I had kids and I haven't built a tube circuit or done much electronics for about ten years. Although my 6-year old is getting interested in electronics, and I found this site doing some research for a project for him. (No 600V tube supplies and one hand in the pocket, just AA batteries :).)

    When I learned tube electronics I was amazed how much had carried over from tube circuits to solid state; that was never mentioned anywhere I'd read, it was as if solid state applications had sprung to life fully formed without decades of tube design preceding it. E.g., thyraton -> scr, neon tube -> zener diode, common cathode -> common emitter, long-tail pair -> differential pair, hexagrid converter -> . . . ok, I'm stuck there, a dual -gate FET might be closest.
     
  4. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    To more accurately reflect what we now know, the following changes have been made to the txt at ibiblio:

    Original:
    Although I'm not sure if this was ever done, someone could have applied the thyratron tube to a relaxation oscillator circuit and control the frequency with a small DC voltage between grid and cathode, making a crude voltage-controlled oscillator, otherwise known as a VCO. Relaxation oscillators tend to have poor frequency control, not to mention a very non-sinusoidal output, and so they exist mostly as demonstration circuits (as is the case here) or in applications where precise frequency control isn't important. Consequently, this use of a thyratron tube would not have been a very practical one.


    REvised:
    The thyratron tube has been applied to a relaxation oscillator circuit. [VTS] The frequency is controlled by a small DC voltage between grid and cathode. This voltage-controlled oscillator is known as a VCO. Relaxation oscillators produce a very non-sinusoidal output, and so they exist mostly as demonstration circuits (as is the case here) or in applications where the harmonic rich waveform is desirable. [MET]

    If you don't like my verbage, let us know what you propose.

    The links refer to the references you mention. They are listed at the ene of the chapter in a bibliography section in the ibiblio copy.

    Some chapters having recent work now have these bibliography sections.
     
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