WA6MHZ
08-03-2010, 02:47 PM
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.
http://farm5.static.flickr.com/4094/4857129422_95fc608f27_b.jpg
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.
http://farm5.static.flickr.com/4120/4857129178_435bf4c027_b.jpg
Now that the box was fabricated, I had to stage the parts.
here is the Schematic to which it will be built.
http://farm5.static.flickr.com/4080/4857129522_fdf8912fde_b.jpg
Not too complicated
Here is the collection of parts that will become the HA-7.
http://farm5.static.flickr.com/4082/4857129286_e3e352c5b6_b.jpg
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...
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.
http://farm5.static.flickr.com/4094/4857129422_95fc608f27_b.jpg
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.
http://farm5.static.flickr.com/4120/4857129178_435bf4c027_b.jpg
Now that the box was fabricated, I had to stage the parts.
here is the Schematic to which it will be built.
http://farm5.static.flickr.com/4080/4857129522_fdf8912fde_b.jpg
Not too complicated
Here is the collection of parts that will become the HA-7.
http://farm5.static.flickr.com/4082/4857129286_e3e352c5b6_b.jpg
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...