1957 RCA 14" model 14-S-7070 TV set

This is not a TV forum, per se. Stereo Theaters, Home Theaters and other three-in-one combination console instruments contain a TV chassis. We can discuss them here, along with stand-alone TV set issues you may care to share.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22260Post electra225 »

There is a lot of online discussion about yoke caps falling apart, but I haven't found a text or video that details the repair of one. So, I reckon I have to improvise. I'm told the location of the centering rings relative to the windings in the yoke is not critical. Close enough is good enough, if that makes any sense. I'm thinking the repair will involve the plastic lid from a mayonnaise jar, the plastic lid from a cottage cheese container, and a cardboard sleeve I use to make Katie Caps. Maybe a couple of strips of duct tape as well. I believe I have an idea how the clips that hold the centering rings can be managed and then how I can get the clamp to hold the yoke onto the neck of the picture tube. I'd think all I need is for the clamp to be just tight enough the yoke doesn't move forward and backward. There won't be anything to keep the yoke from turning on the neck of the picture tube, but I can turn it back to its proper position if it moves. I might even be able to put a couple dabs of Elmer's construction glue in select spots to keep the yoke from turning. There may be changes in this "barnyard engineering" but this is the basic plan. I have found the yoke itself is a lot larger in inside diameter than the picture tube is. I think what was holding it was my inexperience with how much effort the neck of the tube would take, along with the yoke cap being so swollen and melted it was stuck to the picture tube. I believe heating it let the yoke cap come loose from the glass on the picture tube neck.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22265Post electra225 »

I have the caps changed that I have the correct values for. I need new caps for seven paper caps and two electrolytics that I don't have the correct values for. I need four tubes. And a power transformer. My next task is to see if my "barnyard engineering" kluge is going to work for a yoke cover. The yoke looks really good otherwise. The plan is to replace the PT, then run voltage checks without populating the sweep tubes. I'll run the resistance chart again to make sure I don't have an issue there. So far, so good.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22272Post electra225 »

I know you guys like pictures.

The yoke cover fell apart when I got the yoke loose..
100_1058.JPG
I need to invent something so I can use the centering rings...
100_1060.JPG
All you need to build a TV set....
100_1061.JPG
Parts......
100_1063.JPG
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22283Post electra225 »

I am done with the recap project pending sourcing and procurement of parts. I have checked all the resistors. Most are within ten percent of spec. Many are within 5%. Only one was out of spec. Now I'm cleaning controls. The vertical height control acts wonky. I am suspecting tin whiskers, but I'm not sure how to troubleshoot the condition. Resistance readings on this control are all over the place, doesn't give the same readings twice in a row. I have tried cleaning the control with no luck so far. When I had the set running, this control made no difference. I think I have a plan for the yoke cover. I hope Harbor Freight has an inexpensive hole saw kit. I need a 1 1/2" hole saw, and I don't want to give a fortune for one just to cut thru plastic. I won't need a whiz-bang saw for that. After I get the controls all sorted, I need to clean the tuner. I have been advised to use caution cleaning this tuner.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22343Post electra225 »

Pending my sourcing a power transformer, I thought I'd work on creating a cover for the yoke. I really thought this would be fairly simple. The TV guys were right again. It's not. Crist Rigotti made one out of wood, which looks really nice and works really well. I don't have access to woodworking tools anymore. That ship has sailed. I need to kluge up something out of junk on hand, literally junk on hand. I have the plastic lid from an ice cream container, a cardboard roll out of industrial-strength toilet paper, and a plastic lid off a cottage cheese container. This will be my starting point. The plan is to use the ice cream container lid and a chunk off the toilet paper roll to create the cover itself. Put a 1 1/2" hole in the ice cream lid, then glue a 1/2" width of the cardboard roll to the lid. The centering rings have two clips that hold them into place. I don't want these clips to come in contact with high voltage in the yoke, so the plan is to mount them on the cottage cheese container lid and put that behind the cover. I have a smaller cardboard sleeve, one I use to make Katie Caps, that I'll cut a length off of, cut a slot in it, then use it under the clamp to hold the yoke up on the picture tube bell. We'll see how well this works...... ;)
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22349Post electra225 »

I didn't want to spend $40 or more to drill two 1 1/2" holes. I got to looking around in my big tool box and found a 1 1/2 " paddle bit I used when I was running electrical wiring thru studs. The proper, safe way to drill two 1 1/2" holes in plastic would have been to use a round hole saw, chucked up in a drill press, with the work piece clamped to the table, drilling into a scrap block of 2x4. I didn't have that equipment, so I used the most dangerous, most likely to cause serious injury method I could think of. I used the paddle bit in a 3/8" reversible electric, not battery, drill. I found that if I ran the drill forward, the bit dug into the plastic, not only making a weird-shaped hole, but it would tear my arm off or run that paddle bit into the palm of my hand should it slip. I found that if I ran the drill in reverse, the wings on the edge of the bit that starts the hole would score the plastic, then I could just punch the center out. The 1 1/2 inch hole was just a fuzz too small to allow the piece to pass over the bakelite socket on the end of the picture tube. I used a pocket knife, a really sharp one, to hog out the hole just slightly so it would slide over the bakelite socket.

I judged that the plastic ice cream container lid I am using for a yoke cover might be a fuzz too thin so as to not impact the capacitors and resistors on the end of the yoke. I decided to extent the lid about 1/4" to allow for a bit more room without moving it out so far it would interfere with the action of the centering rings. I used one of the 3.5" cardboard toilet paper rolls, drew marks at 1/4" at several spots around the tube, from the end, then used masking tape as a border for my cut. I started the cut with a hand-held jig saw blade, then continued the cut with a single edge razor blade. This to get a nice, straight cut. I then set this ring of cardboard I had just cut in to the first thread on the plastic ice cream container lid. Then I ran a bead of Elmer's construction glue around the edge.

My next task was to kluge up a mounting for the centering rings. I determined that the cottage cheese container lid was too thin. I use plastic containers Swiffers come in and had a couple lids from these containers I had saved to make plastic dial covers from. I found these clear plastic lids were the correct thickness to accommodate the clips that hold the centering rings. I decided to use this extra plastic for the centering rings because I wasn't sure there wouldn't be any arcing between the high voltage in the yoke and the clips on the centering rings. I cut the 1 1/2" hole in the Swiffer lid, placed the cover on, then slid the Swiffer lid on. I drew around the cover with a magic marker. I removed the Swiffer lid with the markings on it, cut around the mark so the Swiffer lid would fit behind the cover. There may be some adjustments that need to be made during final assembly to this kluge, but I believe it is going to work.

The last part was creating a sleeve to hold the yoke against the bell of the picture tube. I cut a 1" piece from the end of a Katie Cap cardboard tube, but an angled slot with a pair of tin snips so it can be clamped around the neck of the picture tube. I had to find a longer screw for the clamp, but I believe this is gonna work just fine. I have pictures that I'll share once I get them loaded to my computer.

I made the yoke cover from scrap junk I hauled out of the trash at the store.
100_1066.JPG
The ice cream container lid was a fuzz too large. This cardboard ring did the trick.
100_1067.JPG
I glued the cardboard ring into the lid using Elmer's glue.
100_1069.JPG
This is the cardboard sleeve I made to hold the yoke in place.
100_1071.JPG
I hope this will work.
100_1075.JPG
100_1076.JPG
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22350Post William »

That looks great, Greg, and in the photos, it almost looks like it could be factory.

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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22351Post TC Chris »

This should warm the heart of all of us who collect odd bits of plastic, cardboard, rubber, steel, copper, etc. because we know some day--usually Sunday night when the stores are closed--we're going to need just the right stuff for an improvised project.

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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22352Post electra225 »

I got the idea from an old Shango video I watched. One from several years ago. He kluged up a yoke cover for an old TV he dug out of an abandoned house, one that had been "sun tested" in the desert sun for 50 years or so. The TV guys 3-D print them, but I don't have that technology. I took my Home Depot tape measure to work and started measuring trash. You'd be surprised to find all the good stuff we toss at the store. I reckon that makes me a hoarder, doesn't it? Seriously, I didn't see any other way to make one. There is a special thrill when you make something usable from items you literally picked out of the trash. This may all be for naught if I can't find a power transformer.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22354Post TC Chris »

electra225 wrote: Thu Jul 25, 2024 1:34 am This may all be for naught if I can't find a power transformer.
Why not post the specs--voltages, current ratings--in case somebody has one in their pile of salvaged transformers? Long ago I bought a GE E-62 table radio at a garage sale. Dead transformer. Found one in my pile. It does run a bit hot, so I've considered using a separate 5V transformer for the rectifier heater to take some load off the big PT.

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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22355Post electra225 »

I can do that. The RCA part number is 1030. 117 volt primary @ 1.38A, secondary 550 volts CT @ 220 ma., 5 volt tap @ 3A, 6.3 volt tap @7.2 amps. The transformer is a vertical mount, but the wires come out the front side instead of the bottom of the side plate. I can put a spacer under the transformer if I find one that the wires come out the bottom. The wires make a bend thru the chassis, then another bend around the vertical output transformer. The issue with a TV transformer is that the high voltage secondary provides a lot of current. This set hasn't got a lot of room for the transformer to be larger than the original. I believe this transformer has 4" X 3" mounting holes. If I have to buy a new aftermarket transformer, I'll get one with a 125 volt primary. I could possibly get by with a 500 volt CT high voltage secondary. I need 245 volts on each plate of the rectifier.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22361Post electra225 »

I may have found a workaround for the power transformer issue. I don't believe, in all the years I have been working with old electronics, I have ever run across a transformer secondary that was only half bad. Typically the whole secondary is dead. One has to be careful getting into a very deep discussion on ARF. If you are a newbie like I am with TV repair, you need to keep your comments in check, or they will devour you like a pack of wolves. Our forum is not a TV repair forum, and I am basically posting this project so it might encourage someone else to dig into a project that might be a tad out of their wheelhouse. I have to give the TV guys on ARF a lot of credit. We have been having a productive conversation and they have been a great help in filling in the blanks for me. The workaround that has been suggested is a "I have nothing to lose" type. I already need a power transformer. If I mess the other half of the secondary winding up doing this mod, I still need a power transformer. Once I get the details down, I think I'll give it a shot. This might help someone on here who runs across a power transformer issue in a console stereo. If you scroll down on page 3, you'll see "irob's" diagram for the workaround.

https://antiqueradios.com/forums/viewtopic.php?t=439605
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22388Post electra225 »

I found the ground wire for the high voltage secondary. I didn't get a lot more done on the TV today, due to a top-priority honey do project. We had an haboob the other evening that knocked down one of the wind chimes and broke it into a million pieces. I put it back together with fishing line and sinkers. That is a story for another day.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22446Post electra225 »

I ordered the parts I need from Just Radios. I am not smart enough to navigate Mouser or Digi-Key websites. I'll do business with a firm that makes it easy for me to spend my money with them. Just Radios has a $25 minimum, so I stocked up on shrink tubing and dial cord to make the minimum order. I ordered two each of the caps I needed.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22456Post electra225 »

The suggested kluge isn't going to work. I need a power transformer. I'd like to find an original part or a parts chassis with a good transformer. The wires are so faded, I can't trace them well. It shows a short from secondary to primary, although nothing is smoking. It draws 10 watts just running the transformer and nothing else. That seems excessive. I have put so much work into this thing, I can't stop now. Surely, I can come up with a transformer that will work.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22463Post electra225 »

I have made a fool of myself on this project. I am in unchartered territory here and I am fumbling along, having a ball. Ignorance is a benefit on this project. The TV guys on ARF have been very helpful with the power supply and power transformer issue. I see that the kluge is back on again. I was measuring AC from the rectifier plates to chassis which no longer works, since the high voltage tap is no longer grounded to chassis. I need to measure with a digital meter from plate to plate on the rectifier.

I am documenting this project on my forum so I can use it for reference in the case that I have a problem and need information to troubleshoot. I now understand a bit more how this modified power supply is supposed to work. I have never seen this mod done before, don't know what to call it, so can't research it. The high voltage tap on the secondary of the power transformer is center-tapped. One side is open. What we are doing now is to use the center tap, originally connected to chassis ground, as one leg of the high voltage tap. The center tap is now connected to pin 6 of the rectifier, the original side to pin 4, plates of the rectifier. I will then connect 600-volt, 1 amp diodes to the plates of the rectifier, connected cathode of the diode to plate pins of the rectifier, anode to chassis ground. The theory of these diodes is this. When positive voltage is applied to the anode of a diode, it conducts. When negative voltage is applied to the cathode of a diode, it conducts. We are dealing with AC voltage on the plates of the rectifier. So, therefore, when one plate on the rectifier is positive, the other one is negative. The diode on the negative-going plate will provide a high impedence pathway to ground. The diode on the positive-going plate will be open, since the diode cathode won't pass positive voltage. The 5U4 rectifier will still work as a rectifier.
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22465Post electra225 »

Pictures to document the power supply mods

Measuring AC across the rectifier plates.
100_1081.JPG
 

Line voltage AC shown on Kill-A-Watt. AC plate voltage shown on digital meter.
100_1082.JPG
It pulls not quite 4 watts from the AC line.
100_1084.JPG
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22469Post TC Chris »

maybe do a rough schematic sketch of the new power supply design, for the dim ones like me who are reading?

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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22471Post electra225 »

Chris, if you would scroll up toward the top of this page, you will find a post with a link to the topic on ARF where they are walking me thru this process. There is a drawing of what we are doing reference the mods to the power supply. That topic will explain it better than I can. I posted that link so I wouldn't have to toggle back and forth between the two forums for details...... ;) :oops:
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Re: 1957 RCA 14" model 14-S-7070 TV set

Post: # 22512Post electra225 »

I have the capacitors done. I have the diodes installed in the power supply. My next step is to populate the tubes and to run the resistance chart again. I have examined my work under a magnifying glass and found no issues. I have checked and double-checked component values. I saved the old capacitors in case I have an issue, I can refer to the pile of old caps. If all is well with the resistance check, I will power up slowly with the sweep tubes out. Vertical output, horizontal output, damper and high voltage rectifier. I will power up slowly with the dim bulb and KAW in line with the power cord. If I power up to full line voltage, and don't let out the magic smoke or cook the diodes, it will be ready to check element voltages.
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