globe scout 680 fc-1

Discussion in '"Boat Anchor" & Classic Equipment' started by KW3U, May 28, 2019.

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  1. KW3U

    KW3U Ham Member QRZ Page

    kw3u here, picked up at auction 5 globe scouts 4 680 and 1 65.
    going over the 1st 2 with dim bulb tester and then full power, i hooked
    up swr/prw meter into dummy load , 80m xtal and key.
    putting out power ok, but in doing voltage measurements around the
    electrolytics i find no voltage on the 3 tab can capacitor which in the 680 manual
    is id'd as FC-1 , I cant find fc 1 on the schematic.
    also the two big 700v caps 12mf at 700v id'd as c14 and c20, i can only find c14.
    will hunt for other manuals but any info on these critters appreciated.
    thanks Jim
  2. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    I love your "mad ham scientist" meets "radio museum" shack pictures on your QRZ page :)

    Good luck with your 680 projects... that's a great old transmitter. I have one paired with an HQ-180 for my "KN7NNN Nostalgic Novice Network" operating position and really like it. Just have to be really careful with the oscillator tuning so you don't tune to the wrong crystal overtone!

  3. W1BR

    W1BR Premium Subscriber QRZ Page

    Did you check the manual on Bama?

    It shows C14 and C20 on the pictorial. I am guessing they changed the design from capacitor input filtering to choke input... or, someone removed the input capacitor to drop the B plus voltage.

    As for the multisection can, you should be able to trace out the connections visually and with an ohmmeter to see where it is used.

  4. WA5VGO

    WA5VGO Ham Member QRZ Page

    It’s been a while since I’ve been inside my 680, but as best as I recall the capacitors are labeled C17, C-18 and C19 on the schematic. In spite of the high voltage ratings, a couple of the sections are merely cathode bypass capacitors and will only have a few volts on them. Double check me on this. I could be mistaken.

  5. NW2K

    NW2K Ham Member QRZ Page

    Regarding the multisection can, it sounds like yours is disconnected. It's common when recapping the 680 to relocate those caps to a place closer to the sockets (6U8, 6L6).

    The power supply was designed to be choke input. It's good that C14 is there. If it's missing, I'd add C20 back in.

    In any case, the original electrolytic caps should be replaced at this time. Why wait? Two, $1 450v caps in series, with equalizing resistors, would do the trick for the two big caps.

    73, Dean
    Last edited: May 28, 2019
  6. KE4OH

    KE4OH Ham Member QRZ Page

    ^^^^^ This ^^^^^

    Just as a matter of interest to somebody ... The "big caps" came rated with 700v working voltage. It's printed right on the cardboard tube. But it's nearly impossible to manufacture an electrolytic cap with greater than 500v or so working voltage. So what did the old manufacturers do? That's right, two higher capacity, lower voltage caps in series up inside the cardboard. Anybody want to guess if they put equalization resistors in there?
  7. W1BR

    W1BR Premium Subscriber QRZ Page

    I've opened them up (to settle similar arguments) and there is definitely NO equalization resistors hidden inside. Regardless, two electrolytic caps of equal value will charge to what is the lowest possible leakage current (it is a series circuit.) One cap will not draw more current than the other and self destruct. Leakage current also rises dramatically if a capacitor is run higher than its manufactured voltage spec.

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