Pi Network, Plate tuning cap, etc

Discussion in 'Amateur Radio Amplifiers' started by K9FV, May 14, 2011.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No, I don't. On the 4-1000A it doesn't matter. On the 8877 I just have a 120 second timer that prevents the amp from keying for 120 seconds after it's first turned on.
     
  2. K9FV

    K9FV Ham Member QRZ Page

    Thanks Tom - That is a big amp!! I'm getting more understanding how to handle the tube placement, tank circuit placement, etc. Thanks to you and others for all the info.

    I think I'll use some ideas from the Ameritron grid/HV protect circuit and add a timer circuit to my PTT circuit to prevent amp from keying for 2 minutes. This will allow HV to anode. Without the amp keyed, there should be no current and ok?

    Thank you again to all for help and info.

    73 de Ken H>
     
  3. W8JI

    W8JI Ham Member QRZ Page

    Big amplifiers are often good examples, because you can "see" things. Also sloppy mistakes that we get away with show up like a bright LED stoplight when high circulating currents are involved.

    If a I build a 1 watt amp it can have all sorts of very gross mistakes and bad wiring and not raise a red flag. If I build a 50kW amp, it better be done correctly or things with even small unexpected loss can cook. :)

    Providing you open the cathode return there can be no significant cathode current, so warm up is safe.

    Check this if you haven't:

    http://www.w8ji.com/bias.htm
     
    Last edited: May 16, 2011
  4. K9FV

    K9FV Ham Member QRZ Page

    Thanks Tom - I read over that page a while back and a lot of it didn't stick at the time due to my lack of knowledge. Now when I read over it, hey - it makes sense!!

    I can see where a QRP amp could handle errors better than a "big" amp could - hey, a few mA of current floating around isn't too damaging, but let a 100 amps go wrong, boy can that cause fireworks!

    73 de Ken H.
     
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