#16
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Continued:
I flattened out the defective coil to roughly determine the inside and outside perimeter dimensions. The approximate thickness of the thickness was a 1/4 inch. I cut a 2.125 x 2.375 x .25 plastic form for a bobbin center. Cut some acrylic squares for bobbin ends and screwed it altogether. I wound a practice coil first with 38 gauge wire. I used enamel wire gauge resistance charts to calculate the amount wire to use for the winding. I based the coil size on the rough flattened old coils' dimensions. After I finished winding the coil, I checked its' resistance and inductance; 345 mh and 725 ohms. This first coil wouldn't work I realized. The inductance and resistance were too great. I was worried about the maximum current the coil could handle also. I had to order a pound of 36 gauge wire to wind the coil with since it could safely handle 70 ma. I over wound the second coil by 125 percent. Ended up using the extra wire to wind a duplicate vertical coil. The motor I use for winding runs at 72 rpm. I calculated the average length per turn of the coil to be 10 inches. This gives 720 inches or about 60 feet per minute. The resistance per foot of 36 gauge magnet wire is about 0.413 ohms per foot. With a needed resistance of about 463 ohms divided by 0.413 ohms/ft , I came up with at least 1122 feet of 36 gauge wire. Took the 1122 feet of wire divided it by 60ft/min , comes to about 18-19 minutes of winding at 72 rpm. In the end I ended up with two coils measuring about 265 mh with a resistance of 470 ohms each. |
#17
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Cont:
To set the new coils in place I used some double side tape. I tried to position each coil toward the front of the yoke, to help maintain the vertical deflection angle. I marked center lines on the coil and yoke to maintain the 90 degree magnetic field between the horizontal coils. Next I used plastic tape, vinyl tape,and finally black duct tape to cover the coils. I wound over 8 ounces of 24 gauge black wire over tape. The black wire core is connected to ground. Tap was wrapped over the black steel wire to prevent shorting of the coil connection tabs. I used some old belt sander fabric to replace the original paper band for connections. The fabric doesn't burn up from soldering. Wrapped 2 turns of friction tape under the fabric terminal band to keep it from slipping. Friction tape was also taped to the underside of the terminal band. I soldered all eight coil wires, resistors and capacitor in close to the same positions they were originally found. I cut some flat black pvc? plastic to replace the old cardboard yoke housing. I heated the plastic in a can over the stove a few seconds to reform it into a cylinder. After I got the coil re-assembled, its' diameter had increased an eighth, but it still fit into its' mounting bracket. I just needed a longer and slightly deformed retaining screw. With the repaired coil installed I started the testing, monitoring voltages, heat and sounds if any emanating from the yoke. Every seemed OK. |
#18
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Some more pictures.
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#19
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These pictures are the results of where I'm at so far, image, quality wise. I still have to clean contacts in the tuner, tubes sockets, and pots. I changed the 108 ohm (measure) cathode resistor of the vertical output tube to increase the raster height. I'm able to get almost full crt coverage. I may have to make adjustments to the vertical linearity RC time constant yet. The set does not have a vertical linearity pot.
I may have to make up a new 16 inch diameter plastic insulator for the crt. The old one was cracked, allowing the semi circular steel threaded strap to ground out the 16AP4. Amazing this didn't cook the flyback. Ed |
#20
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Truly amazing work, Ed. Very impressive! You are giving new life to an unusual set with a yoke made of unobtainium.
Congrats! Clark |
Audiokarma |
#21
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Nicely done!
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#22
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Impressive work! The Zenith vert out transformer I did by hand did not want to work perfectly with the original circuit RC values either...Next time I do something like that I've got to follow your lead and use a motor to wind...18 minutes sure beats my pace.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#23
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Words like Amazing, Fantastic, Gobsmacked don't do justice here. Just hafta do the jaw drop thingy.
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#24
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Thanks everyone for the kind comments.
Now only time will tell how long the yoke will last. Ed Tom, I didn't realize you hand wound that transformer. It took me long enough just to unwind the steel core. |
#25
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Zowie! I have never heard of anyone successfully rewinding a yoke.
Thanks for documenting your process with text and photos. Someday, someone else may be able to follow your lead and save another vintage TV. I'm usually allergic to combos with doors, but I'll make an exception for your classy looking blonde cabinet. Phil Nelson Phil's Old Radios https://antiqueradio.org/index.html |
Audiokarma |
#26
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Quote:
I've been exposed to old TV sets for something like 60 years, especially Motorolas, but I never seen or worked on one of those chassis. Really some strange circuitry. Almost the same chassis that Bob Anderson worked on. BTW, that yoke must use the same steel wire core instead of the ferrites. I only saw one of those. IIRC, it was from an early RCA. |
#27
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Kudos to Ed. I once wound a yoke for a vidicon camera. Fortunately, I had a buddy who had a coil winding machine he built, complete with a turn counter. I used very thin (3/16") plywood for forms. The counter came in very handy when I wound the focus coil. It had 5600 turns!
Is there a link for the schematic? I would really like to see these interesting circuits. |
#28
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Here are links to sections of the schematic showing the vertical output and the HV regulator.
That 35Z5 damper with hum control is another oddity https://flic.kr/p/224WWzJ https://flic.kr/p/23sRc4V |
#29
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Wow. Thanks, Bob. These circuits look like something from a DuMont set. And 37 tubes between the TV and radio!
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#30
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Quote:
The stupid part was it was a only a primary to secondary short...It may have worked fine if I had the presence on mind to unground the one yoke lead before I started the rewind work.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
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