and another...

I've got a 25LC20 chassis - where did those sit in terms of Zenith's development of color TVs? I think it's from '63 or '64 - it uses a 21FBP22. This was right when they were going over to the metal can Xtal, as opposed to the 'tube envelope' one.

It's functional, but I still can't get the color or alignment just right :( But it's had ZERO capacitor replacement. I hate aligning TVs, and hate aligning colors even more. I can barely get the curves shown in the book, and that's assuming the sweep alignment rig works right. Anyone got any hints on a good sweep/marker setup? I have the RCA WR-whatever boxes, they work, but are flakey as heck, and cables EVERYWHERE.

Oh yeah - anyone else with a 25LC20 here? Mine's got 1 core in T4, but the print shows 2 cores and the book seems to suggest it too. Should I assume only 1 was a running change?

The tube is weak, too. Does anyone still rebuild these? I've heard VDC (?) does it, but every time I call....

The color killer is messed up (I suppose MOST of the the set is...) it's more like a 2nd color control than a killer.

But, it works! :) And that's 1/2 the battle.

I have a CTC-16 next to it, that also needs repair, and has by far the most 'nervous' horizontal hold I've ever seen - it jitters back and forth a LOT. It's also not very sensitive, despite being a Nuvistor tunner...

I have in the basement a Sylvania 580 (CTC-15 knockoff). The vertical died on it a while back and I'm too lazy to fix it now (HUGE set).

Was Zenith the only ones who used those funky beam switch tubes for the color?

To my knowledge, Zenith was the only manufacturer which used the 6JH8 "sheet-beam" demodulator tubes; I can remember an old TV commercial from the early 60s boasting of "Zenith's patented color demodulator".

I always thought that the '62-'72 Zeniths had better color than the RCA sets; if you watched a football game on a Zenith, the field was really green instead of a blueish-green.

I worked for a Zenith dealer 25 years ago, and worked on most of their tube color sets. Charlie's picture tube is a rebuilt tube; if it is a Zenith it was probably installed by a Zenith service dealer. The 29JC20 and the later tube Zeniths were much easier to work on than some of the other makes.

Nasa,

VDC in Dallas will rebuild your 21FBP for 165 bucks (not including the shipping). Their phone number is 800-323-9278. Ask for Phil.

He really doesn't like to ship these, but he has come up with a way that he feels will get the tube back to you safely in one piece.

Keep in mind... due to the nature of these tubes being 40+ years old, he will not guarantee you the rebuild will be successful. He has done many 21FBP's for a few of us here on AK with mainly excellent results. But, there has been a failure or two... usually the glass cracking while in the oven. So, it's kinda a gamble on your part. So far, I have brought him 4 duds and 3 of them were a success. He is also currently rebuilding another 21FBP for one of our west coast members.

Phil can give you all of the details when you speak to him.

Good luck!

Charlie, if the rebuild fails or the tube breaks do you still have to pay the full $165?

Eric

Yes, that's the only bad part. He made that clear to me.

However, I had one of my tubes regunned, and it turned out that the new gun itself had a short. In this case, they will try again without charging for it.

Hmm, I'll have to look into that.

Now - when was the 25LC20 chassis made, anyway? Was this early or late in Zenith roundie land? I know pre '64 - the set doesn't have UHF at all (but a click stop for it, but hey! someone stole the strip in that slot!). Oh yeah, any help on what a good sweep generator/marker setup is - mine seems to suck :(

Actually, any hints on getting the alignment would be useful, mine's almost right in B&W, but I'm getting that 'echo' effect on vertical lines, (i.e., a few lighter repeated lines next to it - should I keep plugging away at the alignment, or am I really seeing something in the Y amp that's messed up?). And no color when set for a nice clean B&W pic. Actually, I can get darn near amazing B&W reception on it. But hey, it's a color TV! I want my color, too!

As far as tackling this set capacitorwise - it's got a LOT of those early 'brown drop' epoxy capacitors - like Orange Drops but brown. Are they in the Black Beauty catagory, or are they ok? I've only got a few BBs and such in this set...

Better color than RCA? I'll have to wait until the tube's rebuilt. I'm not sure if this thing's rare earth or not - the screen's that dark green tint when off, and the reds aren't orange on this set. The RCA next to it? Reds so red they're orange...

Sigh...I'm getting there, slowly, I guess...

Zenith chassis years
 

This is something handy that Doug had posted some time ago...

Just so you know, zenith followed a chassis date pattern, in which the first letter in the chassis represents the year of the chassis, like "20Y1C48", in which "Y" is 1968, so:

M 65
N 66
X 67
Y 68
Z 69
A 70
B 71
C 72
D 73
E 74

Although Doug's list starts at 65, it would be safe to assume that the following would apply:

J 62
K 63
L 64

Nasa, you mentioned your set not having a UHF tuner. Did they become standard equipment part way thru 64? Your chassis could be a very early 64 model.

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

I'm not at all sure, but maybe there never was a strip for the UHF position in Zenith TVs made before 1964. I once had a Sams Photofact for the 25LC20/Q (the Q after the model number denoting Space Command remote equipped); the picture of the set on the front of the folder seemed to be of the 25LC20, VHF only.

Generally, the only way to get UHF channels on any TV made prior to April 30, 1964 was to use a UHF converter ahead of the set's own tuner. The VHF tuner was set to channel 5 or 6 to receive the converter's output (whichever was an inactive channel in the set owner's area--either channel 5 or 6 are always unused in any TV market, since the two channels are adjacent to each other) and all UHF tuning was done at the converter.


Some markets, such as Fresno, California, Fort Wayne, Indiana, Youngstown, Ohio, et al. (areas which got their TV stations after the FCC quit issuing new VHF licenses), only had UHF TV channels and still do today. Back in the '50s, when these stations first went on the air, TV receiver dealers in those cities marketed specially-built all-channel sets (and, of course, converters for older VHF-only receivers) before they were available in markets with only VHF stations. I grew up in a suburb of Cleveland and remember when the city's first UHF station (PBS channel 25) went on the air. The year was 1965 and we had just gotten a 17" Sears Silvertone all-channel b&w portable TV. While the VHF reception from our three network stations (channels 3, 5 and 8 at the time) was good, reception on channel 25 was terrible in our area, which was about 30 miles southwest of the transmitters. I later found out what part of the problem was, while watching channel 25 sign off one night; the PBS channel was only running 1 megawatt ERP, and we were trying to watch it just using a UHF loop antenna in our near-fringe area!

BTW, I now live in a definite fringe area for all VHF TV channels and FM stereo radio (45 miles from the transmitters) and have cable for TV, as does just about everyone else here in my small town. The irony of it is, however, that all four of Cleveland's UHF channels (except PBS 25) come in here just great, using rabbit ears. I have discovered as well that the PBS channel I had such problems with back in the '60s (again, channel 25) now has a translator station just about five miles or so from my hometown, and another one not too terribly far from where I live today. I guess translators aren't dead yet.

Another update
 

Finally got the verticle roll to stop. Two black-beauties, although they checked well within specs, evidently just couldn't do the job. They were .01 1000v caps, and while i didn't have any in orange drops, i did find a couple of .01 2kv disc capacitors that i stuck in there. Seem to be holding the picture just fine.

One problem fixed... many more to go! Progress... at least I am making progress!

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.

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?

nudder zenith update
 

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.

Just when things were gettin good...
 

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. :cool:

Now, a new problem has developed. :cry:

Tonight, I was making convergence adjustments, and lost focus and could hear something sizzling. :eek: 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. :scratch2:

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

Figured it out...
 

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. :D

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.

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

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!!!!!!

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.

Re: Figured it out...
 

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.

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.......

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.