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Help Needed: HRO 500 dial mechanism assembly instructions

Discussion in '"Boat Anchor" & Classic Equipment' started by KA9P, Mar 20, 2019.

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  1. KA9P

    KA9P Ham Member QRZ Page

    I'm working on turning an old HRO-500 parts radio into a hopefully useable radio.

    Because of the great posts on the electrical side by KM1H and a few others, I've managed to get the electrical side of the radio working pretty well with some generic germanium transistors and a jumpered on/off switch wafer (still looking for a sub for that...) .

    BUT the radio was originally made a parts radio probably 15 years ago now by a gent that disassembled the dial drive mechanism, with the thought, as he told me, that he could make it smoother. Turns out he lost interest in the project after that, hence it's new home. I'm beginning to see why he may have lost interest :)

    I've slowly but steadily worked towards putting that assembly together in the absence of any diagrams or instructions as to how those pieces go together and have it down to one last problem.

    As best I can explain it, the shaft assembly - after studying the manual and a good HRO (that I can't disassemble) - has a separate rear section that spins with the front section UNLESS a clutch is engaged. The idea seems to be that the engaged clutch holds the front section while allowing the rear section to still turn plus or minus 25 khz to allow for truing up that beautiful 2 speed dial to the nearest kilohertz.

    For reasons yet to be discovered, my rear section turns freely within that +/- 25 khz range all the time. The radio eventually tunes because there is a stop at each end of the adjustment, but when you reverse direction, the rear section doesn't start turning until it hits the other stop.

    In other words, I need to better understand what keeps the back shaft synced with the front shaft when the clutch isn't engaged. I either am missing a part, have misadjusted/misassembled something, or just haven't quite figured it all out yet.

    If anyone has:

    1) any experience with this, or
    2) has an exploded pic of the dial drive, or :
    3) just any useful anecdotal information or suggestions, or
    4) knows someone that still works on these I might buy a telephone consult with, or
    5) a true junker chassis laying around -I might be in the market for the dial drive assembly or the chassis, if priced right-

    I'd love to hear from you, as I'd like to get this radio going again.

    Thanks much for any ideas or leads.

    73 Scott ka9p
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

  3. KA9P

    KA9P Ham Member QRZ Page

    Thanks, yeah, sadly, although National used the same logic for the fast 50 khz/rev on the 500 as all the earlier models, they built in a slow speed on the 2 speed drive, that eliminates the classic gear box and goes to something much more complicated. But thanks for the heads up! 73 Scott
    N2EY likes this.
  4. KA9P

    KA9P Ham Member QRZ Page

    A HUGE thanks to Rocco, N6KN who provided some great notes from his experience with this many years ago that helped me get 500 drive train running despite one apparently missing part. One more ugly old HRO 500 back on the air tonight :)
  5. WB6NVH

    WB6NVH Ham Member QRZ Page

    As above, the dial assembly is NOT the same as all the other, older HRO Type PW assemblies so that data does not apply.
    Note that since this thread was started, coincidentally, the last couple issues of Electric Radio have an article on rebuilding the 500 including the dial workings.

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