Screen/Plate Modulated 50W Input Mod Reactor Question

Discussion in 'Amplitude Modulation - AM Fans' started by W2WDX, Jan 4, 2018.

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  1. AC0OB

    AC0OB Subscriber QRZ Page

    Although I don't see anything special about the QE08, use what you got.

    You either have high voltages and moderate currents or lower voltages and higher currents to get the power you want; it's a tradeoff.

    I would imagine few have heard of the 6360 tube, except for some owners of vintage 2M and 6M transmitters.

    I had 6146's and 2E26's and other tubes I could have used for Beauregard's IPA, but a ham friend of mine gave me a box of tubes and contained therein were three 6360's, so I thought, "what the heck."

    I had never used the tube before so it was a new adventure, but it worked out very well.

    So there.:cool:

    Keep us posted once you get it designed and let us see your schemats.


    Attached Files:

    Last edited: Jan 6, 2018
  2. W2WDX

    W2WDX Ham Member QRZ Page

    I shall, Phil. My ability to make schems right now is messed up. I had software for my PC, but that blowed up, and all I have is a MacBook and no good software to make schems. At least any that have electronic symbol libraries. Don't feel like taking all the time required to make my own symbols. So I have to wait for the new PC.

    On that ... anyone know of good software for an older Mac that has good symbols and doesn't look like a spice schem. I hate the way those look. I tried running Windoze on this Mac using Wine, but it didn't work well on this old MacBook (2007 model w/ 10.6.8 OS).
  3. N2DTS

    N2DTS Ham Member QRZ Page

    You can just use a pencil...
  4. K4KYV

    K4KYV Subscriber QRZ Page

    I find (carefully) hand-drawn schematics easier to read than a lot of computer generated ones.
  5. W2WDX

    W2WDX Ham Member QRZ Page

    I agree. Which is why I don't like the "spice" style schematics. However, time is the issue. Hand drawn takes a while and I can normally draw a schem in a third of the time and make it look better than hand-drawn. I started out my career as a draftsman for a company called Satellite Transmission Systems, so I know what it's like to sit at a drafting table and hand draw on vellum & mylar. I don't want to do that ever again, especially with the software available now. People make the worst schematics on computers, when they could look much better. I don't get that.

    Besides, I don't have any of my templates or mechanical pencils anymore; got rid of them years ago.

    This is the type of schems I used to do before my PC died:

    Last edited: Jan 12, 2018
  6. K4KYV

    K4KYV Subscriber QRZ Page

    With the 22k input resistor, that mic input obviously wasn't designed for a D-104!
  7. WZ5Q

    WZ5Q Ham Member QRZ Page

    I use EAGLE Layout Editor for all my schematic editing.
    It does a lot more then that but makes for a very nice schematic and it's free. Been using it since the 90's so needless to say my image library is large. You can find libraries all over the internet for it in both solid and hollow state.

    All of the schematics I've posted on this forum have been built from that program.
    Here is an example:

    809 AF-67.gif
  8. N2DTS

    N2DTS Ham Member QRZ Page

    100k in the cathodes??? What is up with that??
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    The only compelling reason to use a modulation reactor scheme is to increase the low end frequency response, by minimizing transformer saturation. This makes sense for broadcast stations, but probably not for voice.
  10. K4KYV

    K4KYV Subscriber QRZ Page

    You still need good low frequency response to keep audio phase shifts to a minimum. Poor LF response results in tilting or "canting" of the waveform, which increases the amplitude of audio peaks with no increase in average power. This limits modulation density, since the elevated amplitude of those tilted peaks may push the audio waveform to premature over-modulation. The UTC transformer catalogue recommends for any audio amplifier, near-flat response at least one octave above and one octave below the intended frequency range. So, if you are aiming for 150-3500~ voice frequency range, the speech amplifier/modulator system should be essentially flat over 75-7000~. This is especially important if speech clipping or hard limiting is used in the low level audio stages preceding the modulator stage.

    Some modulation transformers are built with no gap in the core, so use of a modulation reactor is necessary, regardless. I once tried a UTC VM-5 modulation transformer; the thing talked back loudly with the DC running through the secondary. Using a reactor, even though the transformer was designed to be used without one, the talk-back was barely audible.

    Some higher quality modulation transformers designed for use without a reactor can sound pretty good. YMMV.

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