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| Front View |
The major parts are all now fitted in place. The changes in the upper left hand corner for the "EXT KEY" jack required moving the tie point to above the crystal socket. The repair of the off-center hole between the crystal sockets is visible as well, more on that later.
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| Wiring Side View |
The Internal Key:
The little internal key was a weekend project itself. I used acrylic plastic sheet (the stuff in hardware stores is too thin I wanted at least 1/4") a technique called solvent welding. It actually melts a small layer of the material, just like metal welding, and bonds the parts together. It is very effective when joining the polished faces together, not so much the ends. I got my supplies from TAP Plastics:
Qty | SKU | Product | Price | Total |
1 | 10774 | IPS Weld-On 3 Cement (4 oz.) | 5.95 | 5.95 |
1 | 25658 | Small BD-25/2 Hypo Applicator | 3.25 | 3.25 |
1 | 30738 | Polypropylene Funnel | 0.75 | 0.75 |
2 | 00010 | Acrylic Sheets Clear Sample 1/4" (.236) Sample 4" x 4" | 2.00 | 4.00 |
The material is easy to cut and drill, a little trickier to do well. I simply cut a strip slightly wider that the final key and laminated the three pieces together. The center was simply offset and the excess was cut and sanded off when the bond was done. This saved from dealing with two cuts or machining out the center. The trick to drilling was to use the slowest setting on the drill press and remove a small amount at a time. If not, the plastic would build up and/or melt causing the hole to crack out. Probably should have ordered the special plastic bits they sell?
The bottom was not absolutely flat at 90° when I drilled the mounting holes, this caused a slight angle to the long mounting holes. This would have been unnoticed in shorter holes! It would have also been real hard to compensate for on the panel if I had drilled those counter sunk holes first. I ended up enlarging the holes on the key slightly to make up for the difference and drilling where they lined up on the panel.
The arm and contacts are made up of the 18ga. panel metal. For the little bend in the arm; I pressed it in a vice which just happened to have “V” shaped groves for holding work and a bit slightly smaller than the ⅛” axle. I made the axle from a broken ⅛” drill bit shank. Chucked it up rounded and smoothed the ends with a file. Drilled and tapped the holes on a smaller piece to hold the axle and attached using some shortened #2-56 x ¼ ” (3A) pan head screws. I used some of the small semi-tubular rivets for contacts; the small spacers were made from 1/16" aluminum washers filed down on the drill press by placing these in a stack on as screw and milling to size with a file. Electrically, the arm was grounded to the chassis by a short length of fine braid copper wire soldered to the tags. The Key line tag is connected to one of the screws on the "T" shaped tab on the key's base.
The spring was a bit of a surprise how short it needed to be. I cut the spring in half using some wire cutters and bent a hook. It hooks into a small 1/16" hole on the arm and is now temporarily held by a length of paperclip wire. I tried to machine a step but the smaller wire insisted on falling out or getting pulled down the hole. Maybe a flat bottom bit would be better but I think I will cut this wire down and simply heat the small wire with a soldering iron to melt it in place to fasten it permanently.
A little bit ironic I guess; building a 70 year-old radio that the “quiet key” bumper used on the key was a small rubber plug found on the back of an old cell phone! Simply pressed it into a small hole drilled on the arm. The adjustment screw was a #4-40 brass round head screw with a brass locking nut, the hole was located above the bumper and drilled and tapped.
A little bit ironic I guess; building a 70 year-old radio that the “quiet key” bumper used on the key was a small rubber plug found on the back of an old cell phone! Simply pressed it into a small hole drilled on the arm. The adjustment screw was a #4-40 brass round head screw with a brass locking nut, the hole was located above the bumper and drilled and tapped.
The knob is much larger than the original, but it was a 1930’s vintage parts drawer Bakelite knob I thought it was appropriate to use. The only issue is the hole was tapped for a ¼-20 screw! I fixed that by using a piece of threaded rod, an old bolt I think, and screwed it in and filed it flat to the bottom of the knob. Then drilled and tapped a #4-40 threaded hole through the center! It was attached to the arm with a #4-40 "cheese head" screw and lock washer.
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| Another "KEY" part in place! |
BTW ~ I have tested the key on the air already! By attaching it to the external jack and using a ¼” to ¼” patch cord to my Kenwood TS-440. The action was nice and worked OK. It was a little “bendy” but all-in-all OK to use. I first used my added that jack and the key at the same time!
The Hole issue:
This steel is easy to work in some ways but harder in others...literally! Drill bits will wander and miss the required locations if you are not careful. This problem was NOT caused by drilling error. I drilled exactly where the drawing has the mark. The problem was the center hole moved 0.1” from the other holes by accident. I think it happened when I was putting objects in the drawing “on-grid” to line up with the other holes on the drawing. I did not select this as a group of three objects. I did not notice this until I mounted the jacks.
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| Key and Crystal Jack Details |
To patch it I used a counter sink to create a surface to attach solder to. And yes, I soldered it closed and sanded it flat! This may become an issue when I drop the jacks behind the panel; closer to the original design and I need the mounting hole here. We will see how drilling through this patch works out.
De-construction:
Now the hard part: Back on the workbench for tear down! I needed to remove all the parts for counter sinking holes, final finish and rivets. Yes - those modern S/S Philips head screws will be all gone as well.
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| Mk-VII is Ready for Final Finishing |
By the way - Sorry for the blurry pics... but if you notice the light bulbs have different color beads? One of the original glass bulbs was slightly off center and got scored by the sharp metal edge and sheared off cleanly, like a little cap. I think I will keep the parts in case I want to do a LED replica bulb or something.
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