Globe Scout 65A Modifications

Discussion in '"Boat Anchor" & Classic Equipment' started by NN4RH, Oct 7, 2010.

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  1. NN4RH

    NN4RH Premium Subscriber QRZ Page

    I wanted to pick up a comment from this post http://forums.qrz.com/showpost.php?p=2059287&postcount=13 in the "Old Gear on 80 CW" thread without distracting that thread.

    Is there a modification I could make to the Globe Scout 65A to reduce the crystal current, so that I could use the FT-243 cases with the substituted smaller crystals in them?

    I read here: http://www.antiqueradios.com/forums...previous&sid=e83d2ba01e1b35636c5c0cc268cc2c8e that replacing the 6V6 oscillator tube with a 6AG7 tube (with a minor rewire of the tube socket) would have that effect, and might also mitigate the chirp problem besides. Anyone have any comments about that?


    While I'm at it, I saw this article from ARRL archives http://p1k.arrl.org/pubs_archive/55002 that says that modifying a tube transmitter to key only the amplifier and buffer rather than the oscillator tube can solve chirp. The Globe Scout may be a good candidate for that modification if it really works. Any comments?


    I don't want to get too far away from the original design, but on the other hand the chirp this thing makes on 40m is very bad. On 80m it's not so noticable but still there.

    I worry about chirp because in the modern age, it's not as tolerated as it might have been in the 1960s.

    Also, I got an OO card in 1973 because of bad chirp on my first Globe Scout 65A. . . and since getting the OO card scared this then-young kid , I went off the air, couldn't figure out how to fix the chirp, and then didn't get back on the air until 2002! I guess I kind of feel like I owe it to myself and to that OO to fix the problem finally!
     
  2. W8JI

    W8JI Ham Member QRZ Page

  3. W9GB

    W9GB Ham Member QRZ Page

  4. NN4RH

    NN4RH Premium Subscriber QRZ Page

    I'm new at the boatanchor business.

    What is "Oscillator Pulling" ?
     
  5. W8JI

    W8JI Ham Member QRZ Page

    It is like leg pulling, only harder until the pitch changes.

    Another stage or system changes the external loading on or feedback in an oscillator stage and it causes the oscillator to change frequency.

    I'm going to make an effort at expanding that page over the next few days, if I have time. I do not think changing the tube type is a cure for chirp, it can however affect the chirp and if the tube saturates easier it will reduce crystal current and reduce chirp. You could do the same thing by changing values of the two divider capacitors in the Clapp oscillator feedback path (tube cathode).

    I put a 50 mA 12 volt lamp in series with my crystals in the Globe Scout. The lamp acts like a fuse.
     
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