GS35b Anti Parasitic Choke?

Discussion in 'Amateur Radio Amplifiers' started by MM0IMC, Apr 20, 2021.

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  1. MM0IMC

    MM0IMC Ham Member QRZ Page

    I've got a homebrew GS35b triode based grounded grid monoband amplifier, for 10m. I've been told that I don't need an anti parasitic choke of a GS-35B based amplifier.

    Is this true. [​IMG]
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    If you’ve ever built with a GS35b before and everything was done right not suppressor is needed. At times you can burn up a suppressor if it’s designed wrong and still not require one.
     
    WB1E likes this.
  3. KA2RRK

    KA2RRK Platinum Subscriber Platinum Subscriber QRZ Page

    Reading this made my day!

    RRK
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've never used a parasitic suppressor with homebrew amps using VHF-UHF tubes -- they're so stable they don't seem to require one.

    Good example is most 3CX1500A7/8877 amps, like shown below (AL-1500):
    upload_2021-4-21_11-26-50.jpeg
     
    K0UO likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    ^To reinforce this point, an inside view of an Alpha 77DX:
    [​IMG]
     
  6. AG5CK

    AG5CK Premium Subscriber QRZ Page

    I don't see a GS35B in either of those amps. Some tubes, like the 8877, play fine without a suppressor. What's the moral of the story?
     
  7. MM0IMC

    MM0IMC Ham Member QRZ Page

    Thanks for the replies. I've removed the APC and the amplifier seems stable enough.:)
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Those example amps used 8877s, not a GS35B.

    The GS35B isn't even a triode and it's a very different tube...but the point was, it's a VHF-UHF tube with very, very little interelectrode capacitance, a common feature of VHF-UHF external anode tubes. I've found most of them are so stable they don't need any kind of parasitic suppressor.

    Hams use the Russian tubes on HF, but they were really designed for VHF operation, making them good candidates for VHF amplifiers.:)
     
  9. AG5CK

    AG5CK Premium Subscriber QRZ Page

    That's why I was confused. The OP was asking about the gs35b and your examples were 8877 amplifiers. I think you may be confusing the GS35B with something else. It is a triode.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, it is -- I was thinking of the lower-powered "GS" Russian tubes!

    Forgot the GS35B is not only a triode, but an even bigger one than the 8877 is. But, still a UHF tube design. I translated the Russian data sheet (thanks, Google) to see ratings based on tests at 1000 MHz, which is a higher frequency than the 8877 can support.

    As such, I'd think it's unconditionally stable as most VHF-UHF tubes are.
     

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