Heathkit HG-10 VFO off by 2 Mhz higher on 80 meters

Discussion in '"Boat Anchor" & Classic Equipment' started by K1OIK, Jun 10, 2018.

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  1. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    The VFO works fine on 40-10 meters, on 80 meters with L2 slug all the way out the lowest frequency I can get is around 5.5 MHz, the trimmer capacitor only varies a minor amount. Putting the slug in and the frequency goes higher yet. Ideas?
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Several things:

    I have to assume that you got this HG-10 used.

    It may have been that someone has modified the VFO to use with a transmitter that requires a 5.0 MHz to 5.5 MHz input. To accomplish that could come from several directions including removing of turns from the 80-meter coil. Or, the value of trimmer capacitors or fixed capacitors has been changed, You need to look at:

    C-1, C-2, C-6, C-15, C-5, C-10.

    Glen, K9STH
    KM4POK likes this.
  3. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    [edit] Glen beat me to it.... :)

    Could it be that the HG-10 had been modified to work with a modern rig using a 5.0 to 5.5 MHz VFO?

  4. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    L2 looks original, the trimmer does not do much, what possible transmitter could this be modified for? And it also would need to be very stable if done so.
  5. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    I was thinking "external VFO for Split Operation" for most any rig requiring 5.0 to 5.5 MHz Not that I'd expect it to be all that stable, but you never know.

  6. W9GB

    W9GB Ham Member QRZ Page

    The Heathkit HG-10 VFO uses Four (4) oscillator ranges.

    The 80 meter band output is the fundamental 3.5 to 4 MHz.
    The 40, 20, 15, and 10 meter dial scales use the extended 40 meter fundamental 7.0 to 7.425 MHz
    The 6 meter band output is 8.333 to 9 MHz.
    The 2 meter range uses 8 to 8.222 MHz.
    The WRONG Inductor (L2) is being adjusted for 80 meters !
    Do you have the Manual and Schematic ??

    1.) Read Bob Eckweiler’s Summary (link below) to understand HOW the HG-10 works.
    2.) Review the Schematic Diagram, clean version in Bob’s Summary of HG-10 VFO.
    3.) Now, Go Back and properly Adjust L3 (inductor) and C7 (capacitor) for 80 meters.
    Heathkit HG-10 / HG-10B Variable Frequency Oscillator (VFO)
    Heathkit of the Month, #83 : March 2018
    by Bob Eckweiler, AF6C
    http://www.w6ze.org/Heathkit/Heathkit_083_ HG10.pdf
    A Grid Dip Oscillator (GDO) can be useful as well as an L-C meter for troubleshooting.
    LOOK for out of specification components (wrong value, after 50+ years changed value)
    Last edited: Jun 10, 2018
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  7. W1BR

    W1BR Ham Member QRZ Page

    If you are using a counter, make sure it is not triggering on the second harmonic.

    Since it will NOT tune below 5.5 MHz I doubt it was modified. Sounds as if it may be related to an error in measurement technique.
    Last edited: Jun 10, 2018
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  8. W9GB

    W9GB Ham Member QRZ Page

    Appears to be Operator Error (Bench Tech), adjusting wrong inductor (L2).

    PAGE 10, Clean schematic, annotated in RED for function. L3 / C7 for 80 meter adjustments.
    http://www.w6ze.org/Heathkit/Heathkit_083_ HG10.pdf
    Last edited: Jun 10, 2018
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  9. N2EY

    N2EY Premium Subscriber QRZ Page

    Lots of them.

    1) Please read and understand the manual and schematic BEFORE asking questions. L2 is the 40 meter coil. L3 is the 80 meter coil. If you are adjusting L2 on the 80 meter range, it won't have much effect.

    2) Please go over the unit and see if the wiring and components match the schematic and manual. This means tracing out every wire and every component, and checking the values of those that can be checked in-circuit, testing switch contacts with an ohmmeter, etc. Maybe the thing was modified, Maybe it was built wrong in the first place.

    3) Use a grid dip meter to check the resonant circuits.

    4) After you have done the above, if you still have a question, give as much relevant information as possible - not as little. For example: What are you using for a power supply? How are you measuring the output frequency? What is the exact frequency range covered on each band selected?

    IOW, make it easy for others to help you. Do not bogart information and expect others to be mindreaders.

    Yes, all of the above takes time and effort. That's the price of fixing up old radios.
    W7UUU likes this.
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    Very unlikely. Note that the lowest frequency mentioned is 5.5 MHz.

    In cases like this it is important not to go off chasing wild geese in expectation of a quick fix.

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