DX-60B Advice Needed

Discussion in '"Boat Anchor" & Classic Equipment' started by W8TMT, Feb 13, 2020 at 2:15 PM.

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  1. W8TMT

    W8TMT Ham Member QRZ Page

    Just got a nice one at a Hamfest over the weekend, and just starting to gather info. I see stuff on line and on YouTube about adding a relay to provide PTT and "save the function switch contacts" that switch plate voltage in for tune, CW, and AM modes. Why not jumper out this part of the function switch so B+ goes to the tubes at all times (like my HW-16) and pull the grid block keying line to ground with a MIC PTT contact (maybe with some kind of mod to ensure correct PA bias)? Maybe I'm missing something - been CW only on HF since 1974. :).

    Terry W8TMT
  2. W5RKL

    W5RKL Ham Member QRZ Page


    The DX-60 final tube, 6146, is not biased to cut off in CW mode like the HW-16 6GE5 is (see page 55 "Grid Block Keying Circuit" in the
    HW-16 manual). There is approximately 20ma of final tube current flowing in CW mode in "KEY UP" (key not pressed). I don't recommend
    using a jumper wire to bypass the Function switch CW/AM modes.

    The best bet is to install a relay to take over the switching of the high power transformer's secondary 260VAC secondary winding. The
    Function switch can easily handle the low relay coil voltage then switching 260VAC on the HV secondary winding of the power transformer.
    I installed a 6VDC DPDT chassis mount relay below the final amplifier. The relay coil voltage was obtained by tapping the 6VAC filament
    voltage then rectifying the AC voltage in a simple half-wave rectifier. The coil is connected to the Function switch and the 260VAC secondary
    winding wires are connected to "N.O." (Normally Open) relay contacts.

    Mike W5RKL
    heathkit@groups.io Moderator
    EICOTubeAmpsFanClub@groups.io Moderator
    N2EY likes this.
  3. KJ4YEV

    KJ4YEV Premium Subscriber QRZ Page

    I operate a DX60 station. It is completely stock except for a couple audio mods. I did not install any PTT circuitry. I use an outboard relay to key the transmitter through the front panel Key jack.
  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Unfortunately, the switching method used on the Heath DX-35, DX-40, and DX-60 transmitters does tend to cause burnt contacts. At least they finally got a power transformer capable of running the indicated power for the DX-60- series. The DX-35 power transformers failed on a regular basis when the unit was new and the DX-40 power transformer is not all that better.

    Glen, K9STH
    N2EY likes this.
  5. AC0OB

    AC0OB Subscriber QRZ Page

    Both of the above transmitters use grid-block biasing systems, just different implementations.

    The reason the DX-60 final is idling at 20 mA is because of the higher screen voltage in CW mode.

    But aren't you switching the same amount of current through the contacts for the relay as you would without it, since 6V/40 ohms = 150 mA?

    To avoid switching that amount of current one could potentially use something like this to drive the relay and the transistor components could fit on a 2X2" vector board.


    Attached Files:

    Last edited: Feb 18, 2020 at 7:37 AM
  6. K1APJ

    K1APJ XML Subscriber QRZ Page

    I think the problem with the DX-60 circuit is the capacitor inrush when you close the switch. As you point out, 150 mA should not damage anything in a switch of that type. It is curious that the switch fails but rectifier failures are not common in the DX-60.
  7. W5RKL

    W5RKL Ham Member QRZ Page


    The HW-16 is a variable output 90W DC input CW only transceiver.
    The DX-60 is also a variable 90W DC input CW transmitter BUT with "CCSM" AM as an added Mode,
    no internal receiver included. CCSM is short for "Controlled Carrier Screen Modulation". Heathkit, Drake,
    and Knightkit are a few manufacturers use this method of producing AM.

    The final amplifier in the HW-16 "key up" state, biases the final amplifier to "cut off", no manual switching
    required (solid state switching) resulting in no current flows in the final tube in "Key up" state.

    The final amplifier in the DX-60 "Key up" state, however, does not bias the final amplifier to
    "cut off". The final amplifier in "Key up" state still has current flowing. To shut the final amp
    off n the DX-60, the Function switch "disconnects" the final amp screen voltage from the
    B+ source.

    If you bypass the DX-60's Function switch with a jumper wire, current will still flow 100% of
    the time in the "key up" state whether in AM or CW.

    The reason the final amp screen voltage is "reduced" or "less" in AM mode is due to the
    V4 Modulator stage. V4 Modulator stage acts as a "variable resistor" and is wired in
    series between the screen supply and the final amplifier's screen. V4 varies the final
    tube screen voltage at the same rate as the audio signal. Without V4, the final tube screen
    voltage would return to it's "normal" CW final amplifier operating level.

    If you use a jumper wire to bypass the Function switch for AM and CW modes, that's
    entirely up to you. I simply don't recommend it.

    Yes, the relay contacts are switching the same 260VAC secondary voltage. However,
    a higher contact rated relay can handle the switching of the 260VAC secondary voltage.
    From the number of DX-60s with bad Function switches, it appears the Function switch
    contacts are not able to handle the switching of the HV secondary voltage/current.

    The NTE R4 series relays have a 15 amp at 150VAC or 10 amp at 240VAC contact
    rating which should be able to handle switching of the DX-60's secondary HV secondary

    Mike W5RKL
    heathkit@groups.io Moderator
    EICOTubeAmpsFanClub@groups.io Moderator

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