Gs-35b legal limit load cap recommendations

Discussion in 'Amateur Radio Amplifiers' started by KN4CTD, Oct 22, 2019.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Most amps switch in a LOADing padder capacitor in parallel with the variable one on 160m, and often also on 80m.

    Standard practice, and 5kV-7.5kV doorknob ceramic N750 caps are common and handle the job well.
     
    KN4CTD likes this.
  2. W1QJ

    W1QJ Ham Member QRZ Page

    The less lumped capacitance you use on 160 meters the better. When I recently built an 8877 160 meter mono band amp for a customer I used the biggest load cap with the most capacitance I could find for a reasonable price. Whatever you need in lumped capacitance you should break it up in smaller and more caps to spread out the current load. Some Russian surplus honker doorknob caps are very stable and fairly priced. Drifting on 160 is a problem if the wrong type caps are used.
     
    W2VW and KN4CTD like this.
  3. KN4CTD

    KN4CTD Ham Member QRZ Page

    Yes, and that’s the very reason I want to do the same.......to avoid having to stack a bunch of extra caps to get there. I found an air variable from another ham on Ebay that has the wide plates and is spaced at .02” for 1200 volts. It is a 40-1600pf cap. Yes, the wider plates makes it shorter than some of those long, skinny ones. In your opinion, should I go that route for some extra “headroom” as opposed to using the cap from the tl-922......even though I’m always using a good tuner inline??
     
  4. KN4CTD

    KN4CTD Ham Member QRZ Page

    Also, where is a good place to source airdux stock for the lower frequency inductor? I’d like to use that or find a surplus form of sorts to wind my own.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    B&W still sells their "miniductors," and you can buy them.

    But many (maybe most) actually use a toroid on 160m so they can put more inductance into less physical space and use larger gauge wire to do it.
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Ameritron sells inductors used in their amps and tuners.
     
  7. KN4CTD

    KN4CTD Ham Member QRZ Page

    Am I correct in assuming that you’re supposed to measure the gaps on these air variables while the plates are meshed? It looks like my eyeball measurements at the last hamfest I went to came up short. I picked up a NOS Cardwell air variable because it was brand new and cheap but after breaking out the feeler gauges, it looks as if I’m in search of a suitable plate cap also. It only measures .08” good for 3500v peak. I’ll be using 3800-3900vdc no load here so I’m guessing I’ll need something with at least 1/8” plate spacing.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Lou mentioned Ameritron sells their inductors, and they also sell the variable capacitors (including the PLATE tuning caps) and pretty much all other components used in their amplifiers; might be a good source for that capacitor.

    I miss the old Amp Supply Company! Long gone now, but wow they were a great source for amplifier building components. Ameritron has kind of taken up that void.
     
  9. KN4CTD

    KN4CTD Ham Member QRZ Page

    Yeah, I know they sell most if not all the parts for those amps, but for me, it kinda defeats the whole purpose for me. I’m happy that someone sells some of these types of things, but I wish it was more widely available. Purchasing every single major component brand new for a homebrew amplifier doesn’t make much sense to me either....at least not financially
     
  10. KN4CTD

    KN4CTD Ham Member QRZ Page

    I’m a big fan of the classifieds on some of these ham radio sites, but heck, it took me 6 months to find a tuned input board that amp supply used in their amps.....and surely they would’ve produced piles of them.
     

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