Two new Zeniths

I live about midway between Youngstown and Pittsburgh, and am about 35 miles from each one. In this area, I have seen TV sets made as far back as the mid-1950s equipped with factory UHF tuners; we had an old Zenith which had one. Zenith evidently had UHF strips available for their older sets at one time; I have a Zenith 28T962 porthole set from 1949 which has a UHF strip installed in its massive "cement mixer" tuner. Of course, the switch-type tuner used by RCA in the 630 and subsequent sets left the setowner with no choice but to add an external UHF converter.

[nasadowsk]

Nasa, you mentioned your set not having a UHF tuner.

No UHF. Hey, just call me Naz It has a click stop for UHF. The little strip on the turret isn't there, though. The tuner has a jack for UHF tunner input.

Interestingly, I had a Zenith from the 50's that had UHF on it.

Did they become standard equipment part way thru 64? Your chassis could be a very early 64 model.

No idea. I'm running with the theory it's a 1964 or 1963 at this point.

Is your CRT the A version? 21FBP22A? IIRC, isn't the 'A' supposed to signify improved brightness and rare earth phosphors?

I'll have to peek behind there and check. It's not a very bright CRT, that's for sure. I'm not sure if that's a function of it being a wasted (It goes through some fun white point shifts as it heats up, and it quite dim the first few min, plus the focus isn't too teribbly sharp), or not being very bright to begin with. I know the set next to it in my room has rare earths, and it's quite a bit brighter.

The earlier non rare earth CRTs - how close to the NTSC standard were they by this point? I know the 15GP22s, etc were supposedly dead on, but were the later non rare earth types also close?

[Charlie]

This morning I found another black beauty that was the cause of my slightly low HV... i was lacking about 3kv. Now the HV is back up where it's supposed to be.

I took readings off the mysterious HO circuit. The current is within specs... i think it was running about 187ma. At least I know that I'm not putting it under a strain by having a tube in there that the book does not call for.

[Charlie]

Today I got a really good picture out of the Zenith. I found that the AGC was turned up just a tad too much, and after re-adjusting it, things shaped up on the screen very nicely.

Now, a new problem has developed.

Tonight, I was making convergence adjustments, and lost focus and could hear something sizzling. Oh great now what? Anyway, it turns out that the focus tube had a small light show goin on inside it towards the bottom of the tube. I swapped it out twice, but on each replacement, I still have the small light show and sizzling.

Any ideas? What could cause this condition?
Naturally this would have to turn up just when I thought I was nearly finished!

[Charlie]

After examining the inside of the 1V2 tube socket, it turned out that there was a fair amount of corrosion and other crap around the pin holes. I used a small piece of sandpaper and some alcohol on a q-tip to clean it out. Popped the old 1V2 back in and PRESTO! Back in service with no arcing in the tube.

After that, I continued with the convergence. I was unable to do a good job at the top and right sides of the screen. The top just wouldn't come together, and the coils that use a platic hex tool to take care of the right side of the screen seem to be frozen in place. Well, my hex tools are getting a little worn, so perhaps that's why I couldn't get a good bite on it. Maybe tomorrow I'll go buy a new set and try again.

The final result was a lot better than what I started with, but I am not finding the colors to be very rich on all programs. Seems that different stations on the cable have different levels of color. For instance, if I tune in C-span, I have to turn the chroma down a good bit. On most of the other channels, the chroma needed to be turn up nearly all the way for a decent picture. I noticed one channel that the color wouldn't lock into sync, and another channel that wouldn't tune color at all (but yet on other sets there was color). I have noticed the same thing on my cable channels on my CM color set, but it's not so bad that I have to adjust the chroma for each channel.

The picture tube is a little weak on the green gun, but it seems okay considering.

I'm sure that i'll be able to tweak it here and there as time goes on. Maybe I'll find something else that needs changing.

Here's a cable shot from C-Span.

[drh4683]

Charlie,

Nice progress, picture looks great so far. zenith sets are known for that arcing in the 1v2 socket. Both of mine did the same thing, however the sockets were so far gone from arcing they had to be replaced. IN the other set, the socket was already replaced at one time, and I needed to replace it again. What I find works great for preventing the arcing/corrosion is some anti corrosion electrical contact grease. It doesnt conduct, even at high voltage, so its safe to use around the tube pins.
Good luck finishing the restoration

[jstout66]

i think your set has a pretty darn good picture. As for the chroma adjusting..... I know this might seem like a pretty dumb tip, but have you checked EVERY tube in the set and replaced ALL bad ones yet? Some people think that is "overkill" but it tends to make a set operate at peak performance and you have allot less f****ng around to do. I do that with all my sets before I do any adjusting. vacuumtubesinc is a great site to get tubes cheap!!! You've got a great set there!!!!!!

[Charlie]

Originally posted by jstout66
have you checked EVERY tube in the set and replaced ALL bad ones yet?

I found only two zenith tubes in the set, so most have been changed in the past. I've changed more than half of tubes. The B+ is good, so I left the two LV rectifiers in there. Same goes for HV... it's healthy as well. I didn't have the verticle or demodulator tubes, so those haven't been swapped yet. Everything else has been changed.

My tube tester is an old NRI unit... probably from the late 40s or early 50s. It works great, but doesn't have listings for any of the more "modern" tubes used in the 60s. In those cases I just swap it out with a known good one to see if there is any improvement.

[Whirled One]

Originally posted by Charlie

The final result was a lot better than what I started with, but I am not finding the colors to be very rich on all programs. Seems that different stations on the cable have different levels of color.

Picture quality looks pretty good to me, Charlie. Neat looking set too!
As for the problem with the color level changing from channel to channel, this may be a silly question (especially since I'm not familiar with older Zenith color sets), but does that TV even have automatic chroma gain in the first place..? I'm not sure exactly when color TVs first started having that feature, so I may be a bit off base here. The chroma amp does sound a bit weak, though, if you can't get color at all (or color sync isn't stable) on some channels. In any case, readjusting the color (chroma) level control after switching channels is pretty much normal operating procedure for color TVs not having auto chroma gain.

BTW, in response to the UHF discussion in this thread, I believe TVs started becoming available with factory-installed UHF tuners starting in 1952 or '53; it's just that UHF-equipped sets weren't all that popular in many markets until the FCC mandated them in mid-1964.

On a related note, I was just thinking-- just how feasible would it be to alter the tuning range of an old outboard UHF converter to use it as a cable TV tuner instead..? That way you could avoid the need for "modern" equipment (i.e. a cable box or VCR) to serve this purpose.

[jstout66]

my advice if anyone is looking for a good tube tester, is to get a B&K 667. In my opinion those are the best, most durable ones to use when working on tv's. (they're not the best on older tubes used in radios) Anyway, they can be gotten pretty cheaply on eBay and they are small, easy to use, accurate, and durable! Just my two cents.......

[drh4683]

I agree with james. The b+k 667 is an excellent tester for TV use. I have used one, but dont own one. I have a sencore mightymite VII which is from the mid 70's so it has all the odd ball compactrons in the listings. It is essential that your tube tester have the capability of testing for grid emission (or sometimes called "grid leakage") Most tubes in TV's will test OK on emission but will fail grid emission tests, IF and signal amp tubes in particular are prone to grid emission failure. Also, LIFE TEST function is very helpful as this shows the quality of emission if the filament voltage is dropped. Most newer testers have those capabilitys. I like james like to test EVERY tube in a set before I go any further in diagnosis, as you can rule out the tube thing as a potential problem. Even if a set works just fine, I like to test every tube, as some tubes indicate shorts or other problems that dont effect the set, but will over time if not corrected.