RCA 14-S-7070G Horizontal Shrink After Recap

[fsjonsey]

Hey everyone,
I scored a 1957 RCA 14-S-7070G portable locally a couple of weeks ago. I finished doing a complete recap tonight with good initial results, sadly, the 14RP4A CRT is weak.

After running the set for an hour or so, the Horizontal has begun to shrink. I'm guessing a resistor somewhere in the Horizontal section that's drifting as it warms up. The set uses a KCS-102B Chassis. Is anyone familiar with this chassis, and knows where I should start looking for the Shrink problem?

[Eric H]

You might try replacing the Horizontal output tube first, could be fading as it warms up.
Could be a weak 5U4 also.

[old_coot88]

There's a 'quick & dirty' check for identifying a borderline weak tube. It's the "seven seconds off" test. With the set warmed up and showing the fault, turn it off for about 7 seconds, and back on. Is the width slowww to fill back out? That'd indicate a borderline H out tube.

The same test can show up other borderline tubes, e.g., vert out, horiz osc, color 3.58 osc, RF amp etc.

[Phil Nelson]

Hey, great minds think alike! I just finished restoring one of those this week.



The horizontal output tube seems like a good place to start. On mine, that tube had gone to air, and I noticed that it was a replacement Sylvania, not an original RCA tube. So, my set had gone through at least two of them, although the original CRT is still very strong. Maybe it's hard on HOTs, or some other dodgy component stresses them. Of course, everything gets hot inside that tight cabinet.

This is the second 14-S-7070G that I've owned. The first was sold to another collector years ago, but I missed that classy red & gold set, so I grabbed this one when it showed up cheap on the local CL.

I did replace several resistors in mine, including one that had gone completely open, disabling the brightness control.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[fsjonsey]

Thanks for the tips everyone. I swapped the HOT with a NOS Russian 6p31s I had lying around from a amplifier project, and it definitely has improved the horizontal problem. It still shrinks over time, but not nearly as bad as it did.
Phil, I've been visiting your website since I was a kid in the late 90s. I've loved this set since I first saw it on there years ago, and it was a contributing factor to grabbing this one when a customer brought it into the cigar shop looking to sell it last week. We're in an old house located next to an antique store that's also in an old house and people often mistakenly come in with stuff to sell. This time I lucked out. I got the TV for $25 and the lady ended up buying a few cigars for her husband too!

[Phil Nelson]

Well, late 1990s (1997, to be precise) is when I bought my first 14-S. It took me several years of off-and-on puttering to finish that one, but the second one went faster. Here's the new article, for what it's worth:

http://antiqueradio.org/RCA_14-S-7070_Television.htm

Living next to an antique store where people wander in wanting to sell old stuff -- that sounds like a dream come true!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[fsjonsey]

After replacing the HOT and playing the set for a few hours a day, what was left of the Horizontal shrink problem has seemed to cure itself. Maybe there was a resistor that absorbed moisture or something, and playing the set has dried it out? Now I just need to find a good 14RP4A CRT and make a new Yoke cover. This one is partially disintegrated but still holding together enough to keep the centering rings in place. A friend might be able to 3d print a new one for me. A local shoe repair shop is also going to make a new carrying handle for me for $20.

Originally Posted by Phil Nelson

Well, late 1990s (1997, to be precise) is when I bought my first 14-S. It took me several years of off-and-on puttering to finish that one, but the second one went faster. Here's the new article, for what it's worth:

http://antiqueradio.org/RCA_14-S-7070_Television.htm

Living next to an antique store where people wander in wanting to sell old stuff -- that sounds like a dream come true!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Actually, I work at a Cigar Shop that's next to an Antique store. It's almost as good as living next to one, and I get to smoke inside while working.

EDIT:

Also, would there be a way to add some basic form of DC restoration to this set?

[Phil Nelson]

Hey, I love problems that cure themselves. Some coils have cardboard or composition forms that may be affected by moisture. On the 7-inch Hallicrafters TVs, some people take out one little coil and bake it in an attempt to make things right.

Re DC restoration, here's an older discussion of how that might be done in general:

http://mail.videokarma.org/showthrea...=250452&page=2

Let me know if you try that solution on this TV and it's worthwhile. I agree that this set could benefit from DC restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[miniman82]

I know flybacks can hold moisture in them, perhaps yours just needed some operational baking to work well? I saw a video by Shango66 where he put one in a vat of melted wax, and the thing bubbled for a solid 30 minutes!

[fsjonsey]

Originally Posted by miniman82

I know flybacks can hold moisture in them, perhaps yours just needed some operational baking to work well? I saw a video by Shango66 where he put one in a vat of melted wax, and the thing bubbled for a solid 30 minutes!

This flyback looks pretty rough, and the set supposedly spent most of it's life in the deep south, so this makes sense. I watched that shango video too, the amount of water in that flyback was insane.

[fsjonsey]

So I was watching the set last night when I had a sudden, complete loss of vertical deflection. Pulled the back off and noticed that the 6aq5 Vert Multivibrator/Vert Output was red plating. I couldn't hear the characteristic sound of the vert osc running. Popped in another 6AQ5 and the results are identical. Could the Yoke or Vertical output transformer have given up on me, or did one of the new caps I installed suffer a case of infant mortality? I'm going to pull the chassis and have a look around tomorrow when I have time.

[Electronic M]

All possible, but my money would be on an original resistor going open.

[kvflyer]

Yes, if the oscillator is running, you may have lost bias on the grid of the output tube. I would be checking for an open resistor as well.