YO-301 - increasing power handling....

Discussion in 'Radio Circuits, Repair & Performance' started by NA0AA, May 13, 2013.

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  1. NA0AA

    NA0AA Ham Member QRZ Page

    So I got a nice YO-301 station monitor from an SK. I'd like to use it for performing a two-tone test, but the unit is labeled for 500 watts maximum power.

    Now, I think I have the circuit diagram, and I've not taken the covers off yet, but before I do, does anyone have a suggestion for increasing power handling to accommodate my AL-80B?

    There looks like there's one capacitor for the sample pickup on a loop in the coax - would a 3 db attenuator in series with that capacitor do the job?
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    That's subjective whether a 3 db pad would be useful in the YO-301. If you look at the circuit that selects the power
    levels you'll notice C211 is in series with C212, C213, C214, C215. When the selector is placed on the highest range
    the coupling capacitance is just over 1pfd. Making C211 half it's value of 18pfd still leaves the total capacitance at just
    over 1pfd. Meaning you'd have to get about 0.5pfd to theoretically equal 1KW. That means C215 is the target capacitor.
    Instead of using a 2pfd capacitor try using a piece of hookup wire with a twist to two as a gimmick capacitor. If the display
    is too much then untwist and trim the capacitor. If it's not enough then add a twist or so until you get the level of display
    you need.
    Manual here courtesy of the Fox Tango Group; http://www.foxtango.kc9foz.com/Eighties/YO-301.pdf.
    This scope isn't exactly a laboratory grade piece of equipment. It does okay for what it is and what it's meant to do.
    Hope this helps
  3. NA0AA

    NA0AA Ham Member QRZ Page


    Thanks so much for your reply, I have the manual and diagram.

    I see that C212-5 are in a series and that series is tapped for varous values - so you are saying PULL C215 out of the circuit and substitute a piece of wire with a twist?

    I am fairly new to doing this - Google tells me it's two separate wires twisted together.


    I'll pull the cover off and see how much fun this is going to be - I assume that I'd be safe to unsolder only one side of the existing cap and leaving it on the board in case I want to go back and replace it?

    Thanks much.

  4. NA0AA

    NA0AA Ham Member QRZ Page

    Pulled off the cover and found the cap. Then I realized that I am missing one critical ingredient - hookup wire! I don't use it, so all I have is hi gauge stranded and 14 ga magnet wire...I'll have to go to the autoparts tomorrow and see if they have any solid conductor wire. How funny!

    anyway, easy to find and accessible, so I'll get her.
  5. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Yup Eric you use two small wires and one to two twists together should do. It depends on how tight the twists are and the spacing but in general it's just a very simple
    capacitor. The wires never have a direct contact. If you did that then you'd have R900 from a TS-590S.
    The gimmick capacitor is an old trick from days long ago:rolleyes:!
    Have fun
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