Repairing the Heathkit HM-10(a) Tunnel Dipper

Discussion in 'Radio Circuits, Repair & Performance' started by W9GB, Sep 17, 2020.

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  1. W9GB

    W9GB Ham Member QRZ Page

    As many radio amateurs and bench technician has discovered, the GE STD633 tunnel diode (specially made by GE for Heathkit) is rarely the cause of many failures. Rather it is failure of the early 1960s resistors and correct Bias level setting.
    Tunnel diodes, especially germanium, are getting very hard to find and are expensive.
    The 1N2941 may be a replacement candidate.

    BTW the Foam Coil Holder (382-44) rarely survives. Foam disintegrates after 55+ years.
    Heathkit HM-10A Tunnel Dipper Assembly and Operation Manual

    Jeff Avery notes on HM-10A Repair

    Robert Sumption, W9RAS covers disassembly, repair, and restoration
    in four videos (each about 5 minutes) on YouTube.
    Part 1

    Part 3 (Replacing “out of spec” or “bad” parts)

    Jeff Tranter covers the usage of the HM-10a Tunnel Dipper

    Attached Files:

    Last edited: Sep 17, 2020
  2. K1APJ

    K1APJ XML Subscriber QRZ Page

    I had a Tunnel Dipper for a while. It worked OK, but the sensitivity control was fussy at best. there is really no way around it given the primitive DC amplifier design.

    The thing that bugged me, the level of oscillation was so low that it wouldn't do many of the things, signal source-wise, that a "standard" GDO would do. Couple a tunnel dipper to another GDO and use it as a wavemeter to try to find the Tunnel Dipper's signal. It is a tough job. Or, throw a couple turns around the tunnel dipper and try to check the frequency with a scope or counter. Not easy.

    I sold mine and got an HD-1250 instead. But it was fun for a while.

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