Homebrew Hallicrafters HA-7 XTAL Calibrator

Discussion in '"Boat Anchor" & Classic Equipment' started by WA6MHZ, Aug 3, 2010.

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  1. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Having recently scored a vintage Hallicrafters SX-122, one of the best Receivers Hallicrafters ever made, I was dismayed to find it was missing the HA-7 Crystal Calibrator. By themselves, they are very rare, and go for probably as much as the whole radio on Ebay when one does show up.

    I downloaded the HA-7 manual from BAMA (It was part of the SX-122 manual) and surmised what it would take to build one.


    the most difficult part to score was the 8 pin tube like 100 Khz Crystal. BILLEY makes one and one of those came onto Ebay. It went for some SERIOUS dollars, but I now had the critical part to the project.

    Next, I looked over what the box to use would be. A standard MINI BOX would work fine, but it would be difficult to cut the large hole in it for the various parts. I looked at bending some aluminum to do the job, but that also seemed impossible. So, out of scrap aluminum I constructed a box.

    This was very intricate, requiring 14 precisionly cut pieces of metal, 8 metal bends, and 24 flat head screws. That is 48 holes drilled and 24 holes tapped at 2-56 with 24 more countersunk. That took all day to do! PHEW!!! But in the end, I had a perfect MINIBOX with all sides removable for easier drilling and assembly of the parts.


    Now that the box was fabricated, I had to stage the parts.

    here is the Schematic to which it will be built.


    Not too complicated

    Here is the collection of parts that will become the HA-7.


    Today I have all the BIG holes to drill. I have Greenlee punches for the big holes, and the smaller ones will use just regular drills. The bottom plug will have one mounting hole in the center, and then 5 holes to pass the leads through. This is a very critical hole as alignment inside the SX-122 is very tight. It has to be EXACTLY right or it will hit the IF Can.

    a couple of terminal strips will hold some parts.

    Actual assembly shouldn't take too long. The variable cap will be held down with bolts and nuts, and holes in the case to pass the leads through.

    Electrically, the Homebrew HA-7 will be identical to the original Hallicrafters unit, though a 1N34 diode is subbed for the 1N295 the HA-7 used.

    Will continue building today. more to come...
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    WoW look at the size of that slab of rock in that crystal holder.

    What a fun project. :)
  3. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Today we worked more on the Homebrew HA-7.

    First the holes were drilled in the top and bottom. AS EXPECTED, I blew the holes on the bottom and had to redrill those. OH, those EXTRA holes are now VENTILATION HOLES!!!

    The plug was wired on the bottom and I tackled the top plate.

    Using the GREENLEE Punches, I cut the 2 tube socket holes and then drilled the rest of the needed perforations to mount the rest of the components. Some NIBBING of the small angle brackets was necessary but not panful. NOW it was time to wire it up.

    Electronic Assembly of the Calibrator didn't take very long and I "heatsinked" the germanium diode like was needed to be done back in the OLD DAYS.

    Some of the parts were well used.


    The tubes were inserted and the Calibrator was ready for use.


    The Calibrator was installed in the SX-122 and checked out. WORKS GREAT!
    I didn't have to do anything at all, and there was a very loud Cal signal right where it is supposed to be.


    I need to hook the radio up to a good antenna so I can cal it to WWV.

    OK, that project is finished! What can I build NEXT???
  4. KM5Z

    KM5Z Ham Member QRZ Page

    Fantastic job!

    I just this past week did the same thing for a (much less rare) Heathkit HW-32, and I fabricated an 'ersatz' HRA-10-1 calibrator.

    I'd only paid $30 for the radio on Craigslist (non-working, but it's repaired now), so I was hesitant to pay the $30 to $50 I've seen on eBay for the Heath calibrator. But I hated to look at that empty calibrator socket.

    I think I have a total of $19 (for the crystal) in mine, as all other parts were from my stash.

    Mike Yancey
    Dallas, Texas
  5. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Elegant. Thanks for showing us how it's done, and for the encouragement.

    How is the diode heatsinked? I dont' see it.

  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Great Job Pat.
  7. W9GB

    W9GB Ham Member QRZ Page

    Pat -

    Nice work.

    You actually had a couple of options for the Octal plug 100 kc crystal.

    Potter & Brumfield / Tyco makes a clear plug-in hosing (empty) with an octal plug # 543-35D070
    Photo is attached.

    Surplus Sales of Nebraska (most P&B/Tyco distributors should have in stock).

    MODOR Plastics also makes these cases.

    I also have an Octal plug-in (crystal over) used in older Land Mobile equipment that had locations for 2 crystals.

  8. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    I just used a Needlenose pliers tightly clamped to the lead when I soldered the diode. haven't had to do that in years, but thought it would be a good idea for a very sensitive germanium diode. Modern Silicon diodes don't have that problem
  9. WA7KKP

    WA7KKP Ham Member QRZ Page


    Way to do it -- in this day of instant gratification, and too much money chasing the real mccoy on E-pay . . .

    Okay, it isn't Hallicrafters issue, but in the end, who cares? If it works, I'd say it was a good investment of an afternoon of busting knuckles on sheet metal and sniffing the rosin from hot solder.

    Of course, when you're listening to another station, he/she won't have a clue to whose name is on that calibrator. You can smile when you say that line.

    Gary WA7KKP
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