Johnson Ranger audio driver mod

Discussion in 'Amplitude Modulation' started by N8FVJ, Apr 14, 2020.

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  1. W2VW

    W2VW XML Subscriber QRZ Page


    Then there's always the option of making minimal modifications to the RF section and externally modulating the transmitter with a more capable audio power amplifier.

    This is easily applied and reversible in many E.F. Johnson transmitters due to the necessary connections being already available on the accessory plug.

    Transmitters like the Valiant have audio sections which require a lot of attention if one wants reasonable amounts of distortion and an effective signal.

    This method was used extensively by AMers who kept AM alive during the time when ssb was considered universally superior.

    The above route is a relatively easy decision if your transmitter has a 4:1 modulation transformer impedance ratio and modulator tubes which require inverse feedback in order to give reasonable performance. 6146s are particularly bad modulator and linear RF amplifier tubes without a working inverse feedback circuit.

    Some AM transmitters in the 50s were built for use my minimally aware owners. Clipper/filters and anemic modulators were put in place to stop splatter. Today good compression equipment is cheap and available. Different times.

    A Ranger is a different animal as plenty of folks use them to drive a large linear AMplifier.

    If one avoids the technically inferior method of juggling loading and/or screen voltage to lower the Ranger's power, one can enjoy an automatic increase in modulator dynamic headroom with a simple circuit change.
     
    K5UJ and KD2ACO like this.
  2. N8FVJ

    N8FVJ Ham Member QRZ Page

    The Johnson Ranger modulation transformer is likely made with M19 laminations. An option is to go to Heyboer transformer and order a transformer made from M6 laminations and order without end bells. Then, 3/8 longer stack could be used. The M6 and 3/8 longer stack would result in a transformer rated for about 80 watts vs the Johnson 50 watts. I guess the new transformer is about $150 and the old could be sold for $50. If the 100Hz looks bad, I may do this.
     
  3. K5UJ

    K5UJ Ham Member QRZ Page

    I've been watching this discussion evolve and it is interesting from an academic standpoint. In a practical light, you all are talking about a hell of a lot of work for 40 watts. I can sort of see all the drilling and blasting with something like a GK500 where you build it out into a 5 foot rack and wind up with some sort of maul, but the Ranger is an educational exercise only up to a point, unless you have a super good antenna. Otherwise, you can have beautiful sounding audio to a semi-DL antenna and no one will hear how nice it sounds. You can drive a leenyar, but in my opinion, that sort of sucks. The guys running Rangers I've heard straight to antennas are easiest copy if they have the rig set up for D104 space shuttle audio that cuts through adjacent sideband noise, and RFI. You can do minor things to it, but I'd save major stuff like outboard iron etc. for a rig with some scrot. Just my opinion for $0.0
     
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Agreed. I am looking for a WRL Globe Champion 300 or 350 to cover the small Ranger output issue. Some day the Ranger will make a good back up transmitter.
     
  5. W2VW

    W2VW XML Subscriber QRZ Page

    There's nothing wrong with using a low powered AM rig as an exciter into a large amplifier.

    Not a thing.

    That stuff about efficiency is misunderstanding of the numbers.
     
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  6. WA5VGO

    WA5VGO Ham Member QRZ Page

    No it’s not. The efficiency may approach 65% at 100% modulation, but with nothing but a carrier it’s only going to be about 30%. The average efficiency is probably around 45%.
     
  7. W2VW

    W2VW XML Subscriber QRZ Page

    Do a balance sheet for a plate modulated rig. Include all filaments, modulator DC plate input power and driver stages.

    When it's all over those "efficient" rigs efficiency is limited to the class C final. AC mains power for the entire system is not much better than a small exciter followed by a linear amplifier. Certainly not night and day.

    The "efficiency" of the final circuit was part of the rules waaay back when amateurs were rewarded for designing better finals.

    Now it is history.
     
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  8. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    If you're referring to the 6146's Class C efficiency in this rig it is about 71%.

    If you are referring to the linear amp's Class AB efficiency it would approach 65%.


    Pheel

     
  9. WZ5Q

    WZ5Q Ham Member QRZ Page

    That doesn't matter to me.

    My pair of grounded grid 3cx800A7's will do legal limit AM with headroom all day long. I excite this with a low powered, Plate Modulated 809 transmitter that I kludged together from spare parts. This exciter started life as an AF67 but has since been RADICALLY Modified. There is nothing that has not been modified or altered on this rig except for the VFO. I have all the magnetics outboard as most of them are bigger in size then the original AF67. I created this as a temporary transmitter while I build my new shop and can then finish my big homebrew.

    It makes beautiful audio with exceptional modulation linearity and I have no problem being heard.
     
  10. K5UJ

    K5UJ Ham Member QRZ Page

    Hi Dave,
    My prejudices at work here. In my opinion, running a leenyar is a PITA and a real plate modulated transmitter, way way more fun. Operators who never go past the exciter leenyar thing, are again in my opinion, missing out on a lot of the enjoyment that goes with AM. Never gave a thought to efficiency. I run a plastic radio and leenyar on 160 m. It sucks very much and I am looking forward to getting a real transmitter with way less fan noise on that band.
     

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