HEATHKIT HR-1680 issue

Discussion in '"Boat Anchor" & Classic Equipment' started by KM4HNF, Sep 14, 2015.

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  1. KM4HNF

    KM4HNF Ham Member QRZ Page

    I picked up a Heathkit HR-1680 receiver in good external shape, and the inside looks pretty clean also. However, turning on the power via the AF Gain switch produces zero sound or light. Fuses are good, by the way. Transformer secondary shows 25 volts. It appears that someone replaced/reworked the power supply. Looks like they did clean work, but haven't taken it apart to see exactly what they did. I don't think that it is original anyway.

    What I have noticed, is that on the AUD/REG printed circuit board, there are some parts that have been removed or were never installed. Page 97 of the assembly manual shows them to be:
    R201 8500 ohm precision resister
    R202 5000 ohm precision resister
    C201 0.1 mfd mylar
    IC201 78MGT4C
    Q201 transistor heat sink and TIP31 transistor
    F201 fuse holder and 3/4 amp fuse

    There wouldn't be any reason these would have been removed because of the change in the power supply would there?

    Suggestions or opinions appreciated. I ordered a manual, but don't have it yet, and downloaded manual is tough to see the schematic well.

  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    The manual for construction shows that the parts you have missing are exceptionally important, as in, it won't work without them.
    So, yup, you need to locate a supplier for those parts or figure out a way to make a functional voltage regulator in the space the old one was in.

    Construction manual here; http://www.pestingers.net/PDFs/Heathkit_Radios/HR1680_man.pdf
    The description of the power supply circuit is on page 92.

    Hope this helps
  3. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Oh BTW the circuit for the voltage regulation is only applied when using the 120/240VAC supply.
    The battery is supplied through fuse F201. You apply an external 13.8VDC to the two prong plug labeled for that purpose.
    This connector is shown in figure 3-3 of the manual.
    If nothing happens, then check fuse F201 for continuity (which you know it to be open because it's not thereo_O).

    Hope this helps
    Last edited: Sep 14, 2015
  4. KM4HNF

    KM4HNF Ham Member QRZ Page

    Thanks Gary for the info. I looked into the parts, and they should all be easy to find. I see Radio Shack has the TIP31 transistor, and probably most of the remaining parts too.

  5. W5RKL

    W5RKL Ham Member QRZ Page

    I know this is an old 2015 thread. From the initial comments referring to the missing IC201, Q201, R201, R202, and
    the 0.1ufd capacitor, it's possible the previous owner was in the process of replacing that 12 volt regulator
    circuit with an LM7812 regulator.

    A German ham, Michael Reichardt, DL2YMR, has a website that discusses these changes.


    I used Google to translate Michael's German comments/statements into English.

    The changes are simple and easy. They consist of removing and discarding the following components on the AUDIO/REG board

    1. IC201
    2. Q201
    3. C201 (0.1ufd capacitor)
    4. R201 (8.5K)
    5. R202 (5K)

    The following components were added

    1. Two 0.01ufd 50vdc disc capacitors, one disc capacitor is connected between IC201's pins holes 1 & 2 and one
    disc capacitor is connected between pins 3 and 4 (see the AUDIO/REG PC board or Michael's website pictures).
    The capacitor value is not listed on Michael's webpage.
    2. Two jumper wires replace C201 and R201. R202 is removed and discarded, no jumper wire or added component
    is used in place of R202.
    3. An LM7812 replaces Q201. The LM7812 is not a direct pin for pin to the Q201 transistor. The 7812's "IN" pin
    connects to Q201's "C" connection, the 7812's "GND" connects to Q201's "B" connection and the 7812's OUT pin
    connects to Q201's "E" pin. Small wires are used to make those connections. The original heat sink mounts to the
    7812 using the same mounting hardware.

    These are Michael's changes that complete the rebuilding of the receiver's 12V regulator.

    The original dial lamps, 1813, draw 100ma at 14VDC. To lower the current demand, replace the dial lamps with 1819
    28 volt 40ma lamps. Rewire the dial lamp sockets so power for the lamp is obtained at the junction of D1, D2, and C2
    on terminal strip "CC" tab "5". This change provides 24VDC to power the lamps and removes the dial lamp
    current demand from the 12 volt regulated supply.

    The above 2 changes significantly reduces the level of heat in the 12 volt regulator.

    One added comment/request. I'm restoring an HX1681 transmitter and I need the top half of the cabinet and the covers
    for the VFO and final amp. If you have any of these parts or know someone who does have them let me know off forum.
    I'm good on qrz.com as well as my website.

    One more added comment. The VFO can "snag" during rotation. This is caused by one or both
    of the following problems.

    1. The dial plastic Clutch is too loose
    2. The square dial mounting plate mounting rubs against the White dial back plate.
    The fix is to remove the VFO knob and the front Jackson Brother Ball Drive and tighten
    the Clutch mounting screws. Also loosen the White dial back plate mounting screws and
    lift the right edge so the plate rises slightly so the dial mounting plate clears the White plate.
    This problem is evident in both the HR1680 receiver and the HX1681 transmitter as they both have
    the exact same VFO and dial assembly.

    Mike W5RKL
    Last edited: May 17, 2019
  6. AB2YC

    AB2YC Ham Member QRZ Page

    Good info.

    I have an un-built hr-1680 that I mar incorporate this into when I build it.

    Thank you
  7. W5RKL

    W5RKL Ham Member QRZ Page

    I was given the HR1680 and HX1681 twin combination the other day by a generous
    ham. They both are in excellent physical conditions. I experimented using 12 volt LED
    Bayonet dial lamps. I first checked the IC201 temperature with the 1813 100ma lamps
    installed. The heat sink got a bit warm after 30 minutes. I then replaced the 1813 lamps
    with 12 volt LED lamps to see what change/reduction, if any, the IC201 heat sink temperature
    would be. So far I haven't seen much decrease in heat on the IC201 heat sink. I have some
    1819 40ma 12 volt lamps coming tomorrow so I'll try them as well.

    I'm still looking for the bottom half of the HR1680 or the HX1681 cabinet, they are both the
    same size, and the top cover for the VFO so I can begin full restoration of the eBay HX-1681
    transmitter project. Those items are difficult to find.

    Check you HR1680 first. Heathkit made a change in the 12 volt regulator circuit in later
    model HR1680 receivers. I don't know when Heathkit made that change. I have 2 HR1680
    schematics, one have Q201 and IC201 but the other has only IC201 (12 volt regulator).

    Mike W5RKL
  8. W0RIO

    W0RIO Ham Member QRZ Page

    I recently bought an HR-1680 for $50 off of Craig's List and decided that the bulbs were too hot to be
    running that close to the VFO. I chopped up some old PC material and built an LED board, five high-brightness
    LEDs are wired in series with a current regulator circuit. I added two threaded stand-offs to hold the board in place.
    The LEDs reduced the power consumption of the rig considerably and run much cooler than the bulbs. The front panel
    still has that bright red glow. The four LEDs behind the tuning dial were mounted in an arc to provide even brightness
    through the dial.

    The photo also shows the modification I did to the wire between the tuning capacitor and the VFO board,
    I added an extra wire between the second capacitor stator pin and the wire to the VFO board to
    mechanically stabilize the wire. The VFO is quite stable now.

    Here's my current regulator circuit except that there are now 5 red LEDs instead of 2 white LEDs.
    The current regulator is set to 19mA and it drops out of regulation at around 12V.

    AB2YC, KP4SX and W7UUU like this.
  9. K6BSU

    K6BSU Ham Member QRZ Page

    Many of my commercial radios have been modified for LEDs. Mostly to prevent frequent replacement of incandescent bulbs. Also lowers internal cabinet heat. I have a Kenwood tx that requiresd taking a lot of stuff apart just to get to the bulb! But no more.
  10. AB2YC

    AB2YC Ham Member QRZ Page

    Looks good,

    I was thinking about a way to mount LEDs in my HR-1680 (still to be built)


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