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30773Re: [Heathkit:Yahoo] Chirpy HW-16

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  • bobfburns2000
    Aug 21, 2013
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      In a message dated 21/08/2013 19:35:52 GMT Standard Time,
      Lhorton@... writes:

      I thought the chirpy was certainly to be expected with a VF-1 or
      similar, but not with a crystal.Am I wrong?


      =============================================
      Hi Lou

      All keyed oscillators will chirp in one form or another. The old grid
      blocked keying techniques were developed to ensure that the chirp never got our
      over the air. I ran full break-in with a VFO/Buffer/Buffer-Multiplier/PA
      for years in the 60s and 70s with no chirp - just had to get the timings
      right.

      The following is an extract from a document by Ken Gordon W7EKB about HW-16
      Chirp:
      "There are several different suggested methods of minimizing the chirp
      which appears when using crystals with some HW-16s.
      Several have suggested voltage-regulating the oscillator voltage.
      I did this first, and it did absolutely nothing to correct the chirp in my
      HW-16.
      Others have suggested reducing the oscillator voltage by changing the
      point from which the oscillator voltage is taken to 125 VDC.
      I have suggested adding an additional feedback capacitor directly from the
      screen of the oscillator, pin 3 (or 8) to ground.
      I got this information after reviewing several articles from the literature
      on crystal oscillators. It was shown that some oscillators needed
      additional feedback between the screen (which is the oscillator's plate in an ECO)
      and ground. In this type of modified-Pierce crystal oscillator, ground is
      the mid-point between the plate (screen) and grid, since the cathode is
      grounded directly.
      I ended up using 220 pfd, but others have found lower values will work as
      well or better.
      In at least one case, adding a small-value (2 or 3 pfd) mica capacitor
      between the GRID (pins 2 or 9) and ground helped eliminate the remaining chirp
      after the screen capacitor had been added. From a careful examination of
      the circuit, it is clear that this provides a bit of additional feedback.
      Prior to “messing with” the feedback, I also voltage-regulated all the
      voltages to the oscillator tube in my own HW-16: the result was no change
      whatever in the amount of chirp!!
      Adding the 220 pfd capacitor between screen and ground eliminated all but
      a very small amount of chirp for me, only noticeable on 15 meters.
      Another user reported that adding the screen capacitor made his crystals “
      sluggish”. However, when he reduced the value of the added screen capacitor
      to a much lower value, activity returned, and chirp was reduced.
      Another user reported that when he connected an HG-10 VFO to the HW-16,
      and left it plugged into the VFO input jack, but powered off when he used
      crystals, all chirp, even on 15 meters was gone. The capacitance of the coax
      between the HG-10 and the grid of the HW-16 oscillator tube was the added
      factor that eliminated the remaining chirp.
      It is all about proper levels and relationships of feedback."


      73

      Bob

      Bob F Burns G3OOU
      C Eng, FIET, MSE
      G-QRP 6907
      Secretary of Crystal Palace Radio & Electronics Club: www.g3oou.co.uk
      Technical web site: www.qsl.net/g3oou
      @BobFBurns on Twitter: http://twitter.com/BobFBurns

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