Roller Coaster Inductor For Homebrew Amplifier?

Discussion in 'Amateur Radio Amplifiers' started by MM0IMC, Oct 9, 2019.

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  1. AI3V

    AI3V Ham Member QRZ Page

    Pro: will be able to tune on any frequency, not just hambands

    Con: you need a sturdy contact system to prevent above mentioned arcing issues.

    Rege, who used to fix 40,000 and 10,000 watt hf transmitters that used a big roller inductor :)
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page



    View of my old Henry 4K Ultra anode tank roller inductor after 20 years of use, "tuning" up at 1500W output power. Never re-worked or serviced. The amp uses an 8877/3CX1500A7 and produces 1500W CW output power with ~65W drive and is easy on all components.
    Henry roller inductor.PNG
     
  3. W2VW

    W2VW Ham Member QRZ Page

    Cons.

    $

    Lack of optimum Q especially with small turns count. If you do use one consider a series coil for 10 meters. See WIK pic.

    Pro.

    One might be able to avoid those pesky plate load impedance calculations and just Edison the amplifier together.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    In the Henry, the separate coil is actually for 10/12/15m. The big roller is for 80/40/30/20/17m. It is a "continuous coverage" amplifier that covers 3-30 MHz but does not cover 1.8 MHz. It also uses a roller inductor in the "input tuning" network! (A smaller one.)

    I liked that amp a lot, but must admit tuning when band changing was a bit of a chore. Would be perfect for military/industrial/embassy et al. use where they mostly sit on one frequency, and then after dark might switch to a second frequency, but mostly leave it there. For a ham doing rapid band changes, not so much.

    They did come up with an "auto-tune" tube amp a bit later using a 3CX3000A7, the Henry 8K Ultra. That band changes pretty quickly and uses motor-driven components. It was also seriously expensive.:p I think only a few hundred were ever made.
     
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    It is a "pain in the posterior" when changing bands on my Henry / Tempo 2001. However, I do NOT go from one band to another when transmitting. I do have the settings (on the turns counter), for the middle of each band (there are separate positions for the 80-meter and 75-meter bands and the low end of 40-meters and the high end of 40-meters) recorded. That way, after going to the preset position, the amplifier can then be tuned in just a few seconds.

    Although the WARC bands are not on the band switch, the amplifier works fine on 17-meters and 12-meters. However, I use the amplifier with my Collins S-Lines and the transmitters can handle the input impedance on those bands without any problem.

    Glen, K9STH
     
  6. MM0IMC

    MM0IMC Ham Member QRZ Page

    Thanks to all those who replied... I'll be going down the route of the tapped tank coil. I've no interest outside the amateur bands, plus what's been stated regarding roller inductors has been taken on board.
     
  7. W2VW

    W2VW Ham Member QRZ Page

    Are you aware of the trick to find proper taps and capacitance settings with the amplifier cold?
     
    W1TRY likes this.
  8. MM0IMC

    MM0IMC Ham Member QRZ Page

    Is that with an antenna analyser, or something else?
     
  9. W2VW

    W2VW Ham Member QRZ Page

    Antenna analyzer or any continuous coverage HF rig with a built-in SWR meter.
     
    W1TRY likes this.
  10. MM0IMC

    MM0IMC Ham Member QRZ Page

    Thanks for the info.;)
     

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