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Re: mystery regenerative IF stage

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  • John Berry.
    ... IF detector stage. ... stage, just a pot for ... the Detector stage.This can be called the Plate/Anode of the oscilltor of the detector.Does this resonate
    Message 1 of 38 , Feb 24, 2009
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      --- In regenrx@yahoogroups.com, "kyoritsu" <rikkyograsing@...> wrote:
      >
      > Here's an interesting double triode + pentode superhet, with a regen
      IF detector stage.
      >
      >
      > http://www.geocities.com/btse1/6ea8.html
      >
      > The thing is, I don't see any feedback path in the regen detector
      stage, just a pot for
      > controlling the screen voltage. Does anyone know how this works?
      >
      >
      > Rob
      >
      >Hi Rob,is it anything to do with the inductance in the Screen grid of
      the Detector stage.This can be called the Plate/Anode of the oscilltor
      of the detector.Does this resonate around the 1.7mcs of the I.f
      freq' ???.John G1WOS.
    • Jeff Cooper
      ... Well, I ve already made a mess of trying to understand this circuit but the way I (mis)understand it, in a tuned-grid-tuned-plate (of course it s screen in
      Message 38 of 38 , Mar 12 10:13 AM
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        --- In regenrx@yahoogroups.com, "kyoritsu" <rikkyograsing@...> wrote:
        >
        > Can I ask one more question about that circuit? How critical is the value of that RF inductor in the screen grid circuit? Is it contributing to the frequency of oscillation, that is, part of the LC equation? Or is it functioning simply as a RF choke?
        >
        > Rob
        >

        Well, I've already made a mess of trying to understand this circuit but the way I (mis)understand it, in a tuned-grid-tuned-plate (of course it's screen in this case) circuit, there's a tank in the output circuit and a tank in the input circuit. The tank with the higher Q dominates in determining frequency and it seems that would be the input tank formed by the secondary of the IF transformer and its embedded capacitor in this instance.

        You wouldn't want two tanks differing significantly in resonant frequency and each being of high Q. I'd submit that the 750uH RF choke at the screen finds about 12pF of capacitance in the tube, strays, etc. and is broadly resonant somewhere in the neighborhood of the 1700KHz of the input IF transformer (which I assume can be tweaked).

        I think the output of a TGTP can be quite broadbanded which is why I think a resistor instead of the RF choke might still allow the thing to oscillate but I'm not really sure of that.

        But this is all conjecture on my part.

        So how critical? I wonder what the tolerance of that choke is. I'd guess it's not too critical as long as its not high Q. Others can comment but 1700KHz is probably below the choke's self-resonant frequency if it's the kind I think it is.

        Coop, AA1WW
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