Should i bother restoring a zenith?

[Electronic M]

First thing is first on a HV corona/arcing issue (or a restoration for that matter) clean the inside of the HV cage including all parts inside as good as you can without breaking anything(conductive dust and gunk can cause all sorts of arcing/corona). After the cleaning if the issues continue run the set with the HV cage open and or partially dismantled and look for arcing/corona in a dark room with the set on. Once you locate it a picture of the area it is coming from will tell us what it is and how to advise you to fix it.

[Tubejunke]

Originally Posted by Electronic M

First thing is first on a HV corona/arcing issue (or a restoration for that matter) clean the inside of the HV cage including all parts inside as good as you can without breaking anything(conductive dust and gunk can cause all sorts of arcing/corona). After the cleaning if the issues continue run the set with the HV cage open and or partially dismantled and look for arcing/corona in a dark room with the set on. Once you locate it a picture of the area it is coming from will tell us what it is and how to advise you to fix it.

Thanks E.M., that sounds like the logical thing to do. I am sort of jumping the gun I guess as I have the set in a tight spot in the kitchen sitting in the floor on its side doing all the work I can do without being able to move it around much. I guess the good thing about a corona/arch issue is that you can see it in most cases. Removal of the cover and testing the H.V. related tubes will be the next step.

I want to be sure that the fly is running as cool as it should. The ammeter remains connected to the cathode of the H.O. tube, so I can watch for any issues there. I need to run the set for a long enough duration to let things sort of stabilize as they often do. Flys are supposedly notorious for collecting moisture, but I don't really know the symptoms of moisture in a fly.

[Tubejunke]

This set is so unpredictable! I was pleasantly pleased when one day I hooked up a VCR/DVD combo and actually had a clear picture WITH color which had disapeard early on. Next go around or two I used once a stand alone VCR and also an RF converter to try a stand alone DVD player.

Now I have this awful blurry picture with no color at all. The picture has about 4" missing from the top and oddly it will periodically and slowly fade to almost black making you think about HV problems (as I still have the HV hiss and related interference line that it creates on the far left of the picture, top to bottom). However, you can switch to an unused channel and the raster is bright and full as any TV should be.

So I am thinking something in the video or AGC circuits. Any other suggestions? Really this is all dumb when it all could be avoided by replacing the caps and probably having a good running set. Just don't have the time and I hear of so many of these Zeniths more or less working as found. Really, this set is real close to working all things considered. Good sound, full raster etc. Just the HV hissing, video issues, and color. The color can't be far from working fine as I mentioned the one day that everything was dead on pretty much with the DVD/VCR combo.

[Electronic M]

You really should track down that HV hiss. If it has bad enough arcing or corona it can affect HV stability and cause things like the flyback to die....

If you can't see the problem then get some rubber or plastic tubing, put one end in your ear and probe around the HV cage listening for strongest hiss.

[Tubejunke]

The hiss is very, very light which is why I don't refer to it as an actual corona arc, but I guess any hiss is some sort of arc really. Sometimes it clears up on its own. I tweaked the HV adjustment once or twice and it would go away. This was not at an extremely high or a low setting. Just sort of a sweet spot, but it always comes back. You would think that an arc would be significantly worse with a higher voltage.

I shouldn't be messing with that anyway as I don't have a HV probe/meter, but I know approximately where it was set before. I need to find a probe to set that properly. I agree that I need to find the source as the set will never be up to par with that and it's distortion on the screen.

Again though, nice bright raster until a signal is introduced and then it is blurry and sometimes fades to nearly black as if there were HV trouble, but then you can go to an unused channel and everything is normal.

[old_coot88]

Originally Posted by Tubejunke

?...Again though, nice bright raster until a signal is introduced and then it is blurry and sometimes fades to nearly black as if there were HV trouble, but then you can go to an unused channel and everything is normal.

Does the overall raster size appear to 'breathe' or 'bloom' during the fade-to-nearly-black interval?

[Tubejunke]

Originally Posted by old_coot88

Does the overall raster size appear to 'breathe' or 'bloom' during the fade-to-nearly-black interval?

No, not really blooming as I have seen many times; simply fading to black and then it comes back. Now I can say that recently (probably said before) the picture is out of focus when it is there and appears to be bloomed with the top few inches cut off.

Somehow I think a lot of this may tie in with that hissing in the HV cage because it stops sometimes and things are a lot better, but I have had a much better display in the past even with the hissing which only seemed to cause a bit of distortion on the picture and a faint Barkhausen line to the left.

What throws me off is that no matter what I can go to any unused channel and the raster is bright and full with only a hint of the HV distortion when you look real close. That's what I just don't get. I powered the set today in a dark room and noticed a fairly bright blue glow inside the HV rectifier. I'm not sure if that is normal or not. I was thinking that HV rectifiers are normally just dark for the most part. Perhaps the rectifier tube is the problem. I have tested it, but not swapped it. And as we all know tube testers are not testing under real world conditions by any stretch.

Thanks for keeping up on this. I don't have time for a full restoration job and with most all other circuits working well, I don't think that an initial repair of the set is way out of line. If it were a 40s or early 50s set certainly, but these 60s sets can go with a little help in many cases.

[old_coot88]

Originally Posted by Tubejunke

...I powered the set today in a dark room and noticed a fairly bright blue glow inside the HV rectifier. I'm not sure if that is normal or not.

Definitely not normal. If the glow uniformly fills the entire space inside the tube, it indicates a gassy condition. And the tube will usually run abnormally hot.

I was thinking that HV rectifiers are normally just dark for the most part. Perhaps the rectifier tube is the problem. I have tested it, but not swapped it. And as we all know tube testers are not testing under real world conditions by any stretch.

In the case of a HV rect swapping with a known good one is the only real test.

[Tubejunke]

Originally Posted by old_coot88

Definitely not normal. If the glow uniformly fills the entire space inside the tube, it indicates a gassy condition. And the tube will usually run abnormally hot.

I wouldn't say that the entire envelope is filled. By looking up into the cage from below you get a good viewing angle of the rectifier. The glow is inside the thimble shaped portion (plate?)

I want to add that I didn't even realize what kind of an expert is helping me here. I have seen some amazingly well done videos by you on Youtube. It started when I was looking for and acquiring an old tuning eye capacitor tester so I can properly test my old caps. I ended up with a Heathkit C-3, but I am completely jealous of the out of this world unit that you demonstrate in a video. I can't recall the brand, but it had voltage and current meters and you give one heck of a demo!

Also, I remember you admiring your Hickok 209-A VTVM as one of the best pieces that you had on hand. I have one that I really want to get going. Like most older equipment I imagine I will have to replace a lot of capacitors to get it to function well. As it stands nothing about mine is accurate.

Glad to have you on my side in this Zenith project! Maybe I will start a Hickok 209 thread next!

[Tubejunke]

Well, I put the new rectifier in and the situation got better, although the horizontal lines at the edges (about 2"in are more pronounced). The lines are adjustable with the hold control. I used my new probe to adjust to 25Kv. I did it with the brightness down. Not sure if that is the correct method, but it did OK.

IF I can only figure out what is going on with the video and color I would have a decent working set. The lines that I mention I want to call Barkhausen lines but they run from top to bottom, not across. There is a Youtube video where a guy displays issues with HO tubes and Barkhausen lines and sure enough there are lines as well as bad video distortions which is what I have. The picture is not clear and has worms running through it; no color. I guess this is getting to be a good time for pictures. I never tried the new HO tube that I bought as Hickok 6000A (one of the best) does not test these tubes well at all. They have you jump the cap to pin #2 of the octal socket (crazy)! The meter slams and the fuse warning light comes on bright. Also it shows shorts, but so does the new one. I'm afraid that the tester will damage the tubes, so I used my cheap Accurate Instrument tester and they both test the same. The used tube has been red plated a few times and you can shake it and fell rattling. That can't be good.

Whatever is going on is somewhat intermittent as a couple of weeks ago I momentarily had a clear picture AND color, but that didn't last long. I guess this is why people just recap sets and not battle them. I'm pretty stubborn with this one as I know that it is very close to working decently. I haven't messed with color sets much, so I am a little weak on many issues with them.