My First National TV-7M Restoration

[Kc9pos]

Well... after restoring my National NC-183, I have always wanted to have just one tv in my collection. When I was in high school I acquired a 1948 Dumont RA103 that had so many issues that I quickly gave up. Now at 29 years old, I wanted to give it a try again and found that National made a tv. I found an ideal candidate on ebay. I quickly started to clean up and do my research on the tv to set the right expectations for myself. The tv had been recapped before but it had such old capacitors that were probably replaced sometime in the 60s or 70s.



After replacing the capacitors I tackled the resistors, because why not? I am very interested in using this tv regularly which makes me nervous about ‘the hard to find’ 7JP4. I know it will burn out someday. (Anyone ever looking to sell one or has one they wish to part with, I am interested in a backup CRT.) So I threw in a CL-90 rated at 120 Ohm and 2 Amp. Also, for safety, I put in a TVS diode in for the CRT filament to aid in protection and have a little peace of mind.

The next step in the expedition after watching the fantastic videos of
mr. bandersentv https://www.youtube.com/watch?v=dmDd4b8HeUE
was


hahahaha all of them were stiff and stuck and I found NONE absolutely NONE of the lubrications worked from clock oil, to model train gear oil. Even PMX-200 silicone fluid would not loosen it up and allow it to rotate well enough to not feel like it's going to crack off. My guess is the nylon shaft just swelled over time from water vapor and just caused too much pressure inside the resistor.

I love working on this tv set. There is tons of room under the hood and the schematic is perfect for my first time working on a tv set. I know there is always room for improvement on restoration and my set had no prior modifications or crazy setups making it difficult to trace or track down. At this time the capacitors and resistors were replaced, I did not check any of the tubs since I had powered the tv up with the B+ removed and all the filaments did light up. Upon first light, I had no display or audio linked to the high voltage cage. I found one resistor on the 12au7 that I assumed was good and was, indeed, bad at a whopping 8.7K Ohm. After quickly replacing that resistor, I fired the set up and had a line on the screen. WOW!!!!!! So happy indeed.




Messing with the controls, I managed to receive and get in focus the best I could.

At this point I was beyond happy. I felt like I needed to adjust horizontal linearity, horizontal size, vertical size, vertical and horizontal position, and finally the HV oscillator. I was close but then the image went to all horizontal and no vertical. I looked at all the recommended troubleshooting charts and couldn't find a clue. I went ahead and swapped a few tubes and noticed the line going from horizontal now went vertical and decided to grab a tube out of my stock. And bam, like that, I had horizontal and vertical with a raster. I figured it was a weak 6sn7 tube and sure enough, after testing it, the tube was weak. At this point I have the tv operational and trying with my limited setup (because I don't have any equipment for video broadcast) trying to get the best bang for the buck on image. Luckily, I have the bar set high enough, from the great job of mr. bandersentv, I have something to compare to.

I feel like I am very close on finally restoring my first tv set with small items left, like polishing the glass and cleaning the chassis. I am almost ready for reassembly. Audio sounds good and has no issues with audio. I will have to attempt an alignment at some point, just to have closure, but that is uncharted territory for me. I also want to reach out. I do belong to the Hamfesters Radio Club and also have been to a number of Antique Radio Club of Illinois swap fest but I am looking to get more involved, reach out to anyone who is close by who wants to put a good eye on the set, or lend a hand on alignment and optimize it as much as possible. Thank you!

[Jeffhs]

I just read your post regarding your National TV-7M TV. I don't know much about National TVs or radios (my most recent and only experience with National-built gear was with an old US military RAO-7 AM-SW communications receiver back some time in the 1970s; the radio had been built by National, as the small National logo--the letters "NC" within a diamond--proclaimed). In fact, I never knew National even had anything to do with television, until I saw your post.

The company may have produced a few TV sets in the early 1950s after WWII, though; I seem to remember seeing at least one Sams Photofact for a National TV from the early to mid 1950s (my dad had a file cabinet full of them in his workshop in the basement of our house in suburban Cleveland, when I was growing up), but I'm sure that PF wasn't for your set. In fact, if memory serves me, that particular PF was for a 1950s-model 19- or 21-inch console (no remote) with a rectangular CRT.

I do hope you can restore your National TV to operating condition, although to do so you will almost certainly need to replace every capacitor in the set, including, of course, the power supply filters, since the originals are well over sixty years old and have likely failed. This is especially important in the set's power supply, as shorted caps in that section of the set can and will cause serious problems, such as destruction of the power transformer, among other (often irreplaceable) components.

Do not try to power on this TV unless you do so using a variable-voltage transformer (Variac), and be ready to pull the plug immediately if you see smoke or sparks anywhere in or on the chassis. I cannot emphasize strongly enough that you must not power on this TV, or any very old TV, radio, etc. indiscriminately. It will not work, and again, it could be and probably will be irreparably damaged, if it doesn't catch fire or blow the house fuse first.

[Electronic M]

It's looking good so far. I may have a spare 7JP4 available (have to find it).
It's possible we have crossed paths at ARCI before....I sold a Sylvania halolite console the last Radiofest (and picked up a Danish modern predicta) and had it running off a 70s wards gas generator at the meet.
Jim Mening (Wisconsin here here on VK), Bob Anderson (Banderson here and YouTube), and Doug Harland (drh4683 on YouTube and occasionally here) all usually attend Radiofest and we know each other.