QCX 40 Meter QRP rig Question

Discussion in 'QRP Corner' started by AC8UO, Apr 1, 2020.

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  1. AC8UO

    AC8UO Ham Member QRZ Page

    Hello Fellow QRPers,
    I recently purchased a QCX 40 meter QRP rig. I would like to power it with a Pyramid regulated linear power supply. (13.8 V DC, 2.5 AMP constant, 3 AMP surge). Would this be an adequate power supply for this rig? Thanks in advance for any advice you can provide.
    Dennis, AC8UO
  2. AC8UO

    AC8UO Ham Member QRZ Page

    Sorry. I already asked this question and received excellent, helpful replies. I would forget my head if it were not attached.
    Dennis, AC8UO
    AJ6KZ likes this.
  3. N8AFT

    N8AFT Ham Member QRZ Page

    TX current draw is 514ma according to the manual.
    Google QCX40 QRP to find web page, manual is there.
  4. K5DH

    K5DH Ham Member QRZ Page

    The QCX is an amazing little rig. A lot of performance for $49.95, and fun to assemble (although it was made somewhat more difficult by my old eyes and "gorilla" hands, hi!).
  5. N1ST

    N1ST Ham Member QRZ Page

  6. K5DH

    K5DH Ham Member QRZ Page

    My QCX-20, in a Velleman plastic enclosure:


    Don't forget to include a 1 Amp fuse in the (+) lead of your DC power cable!
  7. K5BEZ

    K5BEZ XML Subscriber QRZ Page

    my QCX is on the way! Can I get some info about the Vellman enclosure?
    thanks in advance.
  8. K5DH

    K5DH Ham Member QRZ Page

    The enclosure is a Velleman G738. They cost about $16. Not many places sell them, but search around on the internet and you'll find those that do. I got mine from a local electronics store a couple of years ago. Sadly that store is no longer in business.

    This is not a "drop in and go" arrangement. You'll need to do some homebrewing. My board is mounted in the case on four short threaded standoffs that came from the junkbox. I cut out the opening for the display using a fine-cut cutoff wheel in my Dremel tool. I drilled all of the holes for the controls and connectors. Measure carefully before you drill! The square hole in the right side panel for the antenna connector had to be filed to shape.

    You can see that the two knob shafts do not protrude through the case, so I had to find some usable knobs. Mine came off an old Sears CB radio. One of them had to be shortened. I cut it down using a fine-tooth X-Acto razor saw.



    Here is an overall view of my QCX opened up. I'm using a 2.1 mm coaxial DC power connector. The fuse holder came from an old HyGain CB radio. The power leads are soldered to the underside of the QCX board beneath the green terminal block. The power leads are #20 AWG wire.


    The two tiny SPST NO pushbutton switches came from that same now-defunct electronics store. They are threaded directly into the plastic case. #24 AWG wires connect them to the QCX board. The holes for this are already provided on the board. The switches are in parallel with the ones on the QCX board.


    In stock form, the tab on the 7805 voltage regulator is too tall for this enclosure's lid to fit properly. I had two choices: (1) make a hole in the lid to clear the 7805's tab, or (2) modify the 7805 to lower the clearance. I chose (2). I used a tiny flat jeweler's file with fine-cut teeth and carefully filed down the 7805's leads so that it would sit flush on the QCX board. Dropping the regulator down onto the board gave enough clearance for the enclosure lid to fit. You can see in the photo that the top edge of the tab is just lower than the black plastic side panel. This regulator lead modification could also be done using a fine-cut cutoff wheel in a Dremel tool (but work carefully; those leads break easily). Do not grind off the 7805's tab to gain clearance. It's required for cooling!


    I pulled a spare 7805 out of my parts bin to illustrate what I'm talking about. The arrow points to the thick section of the leads, which must be thinned down. I tried to draw yellow lines on the leads to show how they need to end up, but those lines don't show up very well in the photo. Suffice it to say that all three leads must be thinned down, all the way to the regulator body.


    Again, this is not a drop-in solution. But it wasn't that much work, and the end result is pretty nice! I hope this information is helpful. I don't expect anyone to exactly duplicate what I've done, but maybe this will get your "creative juices" flowing and help you come up with a workable solution.
  9. K5BEZ

    K5BEZ XML Subscriber QRZ Page

    Thanks for the info Dean!
    I really appreciate it.
    I have no problem with drilling the necessary holes etc..I'll search the interwebs and find the G738
    73 de Brett/K5BEZ
  10. K5DH

    K5DH Ham Member QRZ Page

    FB, Brett. Let me know if I can help.

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