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  1. #1
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    AGC in tube reflex and regen

    Hello I am trying to build a tube receiver shown here http://www.qsl.net/k5bcq/REGEN2/regen3.html

    I have built the circuit but I would like to convert the audio amplifier so that it uses some kind of feedback from the output back to it's input so that it greatly amplifies the audio signal.

    Reflex receivers do that but I would like to split the circuit into two tubes because I also need to have AGC.

    What I am thinking is to have positive feedback to the input of the AF amplifier for a huge audio gain and negative feedback to the input of the RF amplifier to controll the gain.

    Are there any tube schematics out there?

    •   Alt16th July 2010, 08:40

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    AGC in tube reflex and regen

    Your idea isn't well considered. Reflex concept works for small band RF, basically increasing the Q of the resonance circuit.
    Of course today's EMC rules are strictly contradicting this pre-World-War-II technique.

    But it can't work for AF.



    •   Alt16th July 2010, 09:04

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    Re: AGC in tube reflex and regen

    Ok, I am trying to build a simple tube set (tube for cosmetical reasons basically) which operates on 12V. I have successfully built the circuit shown and the performance is good in terms of selectivity and with good RF sensitivity as I can listen quite distant SSB stations.

    In order to make it more audio amplified I am thinking of "borrowing" the principle of reflex audio feedback, but using the second tube only. The advantage of using a second tube is that you can have positive feedback to the audio amplifier (second tube) and at the same time negative feedback to the RF amplifier.

    apart from AGC, all I need is an audio amplifier schematic that will be able to achieve a high gain using feedback loop.

    Any thoughts/schematics?



    •   Alt16th July 2010, 09:25

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  4. #4
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    Re: AGC in tube reflex and regen

    Schematic looks wrong to me.

    Check the two grid connections on the output stage are not reversed.

    Brian.



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    Re: AGC in tube reflex and regen

    I have build a completely different audio stage so I do not know about its performance.
    The AF section has been build differently. I have used an ECC86 in single ended triode amplification (one section follow the other) and then a 12K5 for final, which gave me a low volume on a small speaker (around 250mW audio output best).

    Since my audio amplifier uses triode and tetrode I would not to post the schematic.
    Anyway I have used this audio amplifier following the regen detector: http://www.sophtamps.ca/schematics/sopht_12k5-v6.jpg



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