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Plate Modulate a Tube CW TX

Discussion in 'Home Brew' started by T23, Dec 17, 2011.

  1. T23

    T23 Active Member

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    I have a Heathkit HW-16 that I would like to get on AM phone with. I have been doing some research. So basically do I just put a modulation transformer in line with the plate voltage input of the tube? (what is pin 6 on the 6CL6) Also should I modulate the driver or the final tube? The tube line-up is 6CL6 osc. 6CL6 driver and 6GE5 final.


    T23


     

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  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Pin 6 on the 6CL6 is the plate. For true plate modulation you connect the secondary of a modulation transformer in series with the B+ line and the plate lead of the tube. The primary of the mod tranny is connected to the audio input source.Properly done requires knowledge of the plate input impedance as well as the impedance of the transformer's primary and secondary windings and ideally things should be matched. In this case however with such low power involved it should not be a big deal. A tube like the 6CLC and even the 6146B is usually grid modulated for carrier controlled type modulation rather than plate modulation due to the fact that with that method the tubes actually "rest" better between voice peaks and it is easier of the tubes due to less heat.
     
  3. T23

    T23 Active Member

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    Ok, I see. I was looking into grid modulation too, but saw that at voice peaks the output actually dropped of, negative swing if you will. So it looks like. I'll modulate the driver then.


    T23
     
  4. T23

    T23 Active Member

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    If I were to grid/screen modulate this transmitter, would I connect the modulation transformer the same way? It might be better. This way, I believe the voltage is lower on the grid.

    T23
     
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Something for you to check out.

    Control-Grid Modulator

    I'll try and explain it in a bit. I'm busy right now changing out the display screen in a laptop and only came here by mistake while searching you tube for how do change the screen. :laugh:
     

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