Zenith 15L37 "karmic restoration"

[DavGoodlin]

Hi all,
After following this site for two years and gathering, rather than tackling projects, I came upon the perfect project to dust off my skills and gain some tech-confidence before I restore my older sets with the required thoroughness, especially the RCA 721TS and 8T241 I got a few months back. Times have changed because I actually had to BUY these 1940's sets.

Projects used to find me all the time, well they still do, just not something with tubes In my parent's basement was a 250sf workshop full of stuff BROUGHT in before I could even drive. Imagine that. It was long time ago when I made TV's work again just for fun, then I moved out to attend tech school and actually had to make a living at it. Now I make time for it with a clear goal. I wanted to watch the so-called "Debate" last week on a pre-65 black and white set, then realized all of my sets needed somethingmostly time.

In June, I was presented with a 19" Zenith BW in a metal cabinet similar to one I gave away many years ago. Here's where the karmic wheel started: The set I gave away in 1977 had been at my Aunt's farmhouse, on the front porch, just out of the rain. It sat there year after year on an old pedal sewing machine, dutifully waiting for the season, just like a fan or air-conditioner. My uncle would pull out the rabbit ears and watch the Phils or Orioles while enjoying spring weather, among other things. After a few years of me showing up randomly and plugging it in just for kicks, marveling at how it worked perfect after sitting all the wet winter and sticky summer with mold growing on the faux fabric contact-paper covering the metal cabinet, they said "take it home this time!" I did almost nothing to it, then used it nightly for 6 months. Then a friend of mine needed a TV so I let him have my 1952 Motorola 17T6. Since I only did a half-ass recap on it, it did not last long. I then let him have this Zenith and I still have that Moto today, good CRT but un-finished.

The wheel has come around with this model L2108, a gray-painted metal set with a now-broken handle as it almost tumbled down my attic stairs. Lesson 1; do not trust a 48 year old handle on a "luggable" set.
Now for the minimal intervention needed. It came to me as a working set but traveled from Buffalo, NY in a trailer with a shipment of test equipment and books I had bought via email. It then bounced in my truck the remaining two-hour trip over the mountains from Shamokin. It did not power up, so the circuit breaker was the primary component of interest. I found a correct "Littlefuse" replacement of much better quality and soldered it in like the original. The I saw this before replacing anything else 15L37 on1.jpg

The sound buzzed, even after adjusting the buzz control, sound IF, takeoff and limiter coils. The vertical size/lin was adjusted to fill the screen but not linearly. Then the the "wave" started, slowly, then getting worse after just a few minutes. So I copied sams 702, highlighting electrolytic caps I needed to order 9-20 063.jpg and then flipped it over to remove the bottom cover and see to what extent I needed to replace paper caps. Imagine the surprise when I saw only two bumblebees and no white tubes, one of them a .015/600 6GK6 plate to feedback, the second a bypass off the 6GV5 screen grid at the width control. Then I looked and spotted a third cap just to be safe, the .1/600 volt maroon drop between 700 volt boost and B+270v. This was probably OK, but I replace anything around the flyback or Vertical output transformers to be safe. It is rare for the mica/disc caps to be bad, so I leave them alone.

I needed NO tubes, hell I didn't even test them, they were all Zenith, except the 6GK6 vertical output was an RCA. I found a Zenith 6GK6, tested it and swapped it in. So I ordered the caps from Allied (this time) and heated up the 40watt soldering pencil. I disconnected all the power supply electrolytics and tucked the new ones in. (2@47uf for an 80 uf, etc). The low voltage electrolytic capacitors were simply bridged to save time. I never had those short, just open. These were located in the AF out 6AQ5 cathode and plate circuits, the Vert out 6GK6 cathode (fixed the linearity) and AGC/noise gate 6BA11 cathode (I think this one fixed the sound buzz) To finish up, I added a CL-90 line thermistor to limit inrush currents when switching on.
15L37 under.jpg15L37 rear.jpg

All done and the only thing I suspect now is a weak 1K3 HV rectifier since the picture blooms a bit when I increase brightness. The width control is set for minimum and its still too wide.
15L37 on2.jpg

The Sylvania Sylouette Halolight is next and it will be a CAP-FEST compared to this one.