Should i bother restoring a zenith?

[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!

[old_coot88]

TJ,
'Fraid you've got me confused with confused with another person. The fella posting the cool videos is not I. Perhaps he could chime in and say Hi. (Hey that's a po'm.)

Regarding the problem with your set, in a shop setting the very first move would be to replace the HV rect, to eliminate that as the source of the problem.
But barring that, feel the tube after a few minutes' running. A good tube should remain just a little warmer than ambient temp. But if it gets sizzling hot that would indicate a problem.

[Tubejunke]

Originally Posted by old_coot88

TJ,
'Fraid you've got me confused with confused with another person. The fella posting the cool videos is not I..

Oh, OK; sorry about that! There is such a person who uses the same screen name as you and bears a plethora of knowledge.

Anyway, I think (HOPE) that I have a sub for that rectifier in my much too large collection of tubes. I started a thread in the classifieds looking for a HV probe/meter so I can properly set the HV. So far only one person has responded and he has something that I can connect to my Simpson analog VOM, but it maxes out at 25Kv which is (I think) where the HV should be.

If it is indeed 25Kv, then I could use the instrument, but would need to be careful not to peg my meter if the voltage were too high. Just turn it down and work up sounds like a plan.

[old_coot88]

Originally Posted by Tubejunke

...If it is indeed 25Kv, then I could use the instrument, but would need to be careful not to peg my meter if the voltage were too high. Just turn it down and work up sounds like a plan.

Even if goes to 30KV, it ain't gonna prang the meter movement any moreso than turning the R zero adjust overscale.