Color crt testing?

[Tubejunke]

My 1964 Zenith has a rebuilt Sylvania CRT. I have an Accurate Instrument tube tester with CRT emissions test capabilities. Before I go on, I will note that this set has not been powered up in around 25 years and has not been used since the 70s until I brought it home several months ago. Anyway, when I performed the test the red and green guns were immediately strong, but the blue gun was not really bad, but much weaker than the other two. I have read stories about long dormant tubes sometimes taking some time to pop back to life; I hope that is my case! What I did was bump the filament voltage up to the next setting for maybe 20 seconds on the blue gun. Naturally, that bumped the reading up and I feared that it would just settle back once the correct voltage was re-applied. Well, it did settle back some, but what I did appears to have helped a lot! The blue gun now maintains a higher reading.

In summary, I guess I am wondering if the blue gun is often a bit weaker perhaps because it bears more heat than the other two being positioned on top. The Accurate tester is a bit confusing because the instructions say to use the "diodes ok" scale which is almost ALL in the green except for maybe the first 1/4" of needle deflection which is red, or bad. ALL of the readings were far from the red from the beginning. I prefer to look at the numbered scale for comparison purposes. The blue gun reads maybe 45, where the other two guns read like 60, but going by the instructions the tube is deemed good either way. As long as I can achieve a good color picture I will be satisfied, but I don't want to put any money in the set if the tube is on it's last leg.

It's funny that nearly all of the section tubes are stock Zenith tubes, but the set ran long enough to go through the original CRT. Perhaps the local repair shop used stock replacement tubes.

[miniman82]

The position of the gun has nothing to do with emission, any gun can go weak for a multitude of reasons. I have a CYP with a nearly dead green gun, while the other 2 don't leave the top of the scale no matter how long I hold down the life test button. It's an RCA rebuilt Colorama.

[andy]

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[DaveWM]

You can do a lot with the screen and gain settings to get a decent pic. I would not do a thing to the CRT until all other avenues have been explored.

I have one zenith that just takes a couple of mins for the colors to all come up, but after that its fine. Its not like you can go out and get a replacement CRT so why risk it if it works after a few min run time.

[oldtvman]

If you do need to restore a crt it is best to put the crt on it's face to avoid any residue from landing in the gun assembly.

[zenithfan1]

Just wondering, since it's been through one CRT I'd bet you are right about some of the tubes being replaced with Zenith tubes. The way to tell a factory Zenith tube from a replacement is: factory tubes have yellow print while replacements have red print. That way, the techs knew what ones were changed by them on the service contract. Is there any with red print in there?

[Tubejunke]

Originally Posted by zenithfan1

Just wondering, since it's been through one CRT I'd bet you are right about some of the tubes being replaced with Zenith tubes. The way to tell a factory Zenith tube from a replacement is: factory tubes have yellow print while replacements have red print. That way, the techs knew what ones were changed by them on the service contract. Is there any with red print in there?

No red print. I have the back cover on right now, but I would remember if they were red print. They were yellow, or posssibly white.

[Tubejunke]

Originally Posted by andy

If you do want to rejuvenate it, get a more modern tester if it's older than the 70's. The old ones do more harm than good, but it's often amazing what you can do with a well designed rejuvenator. I love my Beltron, but a modern Sencore, or B+K should be just as good.

I would LOVE to have some modern test equipment! My funds are ULTRA limited right now. That is why I haven't started replacing caps in the Zenith 5111! I just brought in a Hickok Model 532 tube tester (no CRT) with three sets of scrolls. The oldest is dated 1950 and the most updated one which is in it is dated 1961! It, like all of the other Hickok equipment that I have has a multitude of settings and a ton of switches etc. It looks like something off of an old SCI-FI movie, but I am not trying to start a Hickok collection (which I seem to have). If anybody can direct me to somebody into vintage test equipment, perhaps I could come out on top for once and land a modern B+K or Sencore tester AND a decent oscilloscope. I know that the Hickok stuff is very desirable. If nothing else I could sell and just buy what I need.

[Tubejunke]

Thanks to all of you for the advice! Sometimes I start a thread and it gets very little feedback. I guess it depends on the subject. I do understand that it is hard to diagnose or troubleshoot anything over the WWW or the phone. I used to work in auto parts and the public expectancy of a parts clerk to give them the magic answer, or training over the phone, or even outside in the rain was rather ridiculous! Here at VK it never hurts to throw something out there. You never know who might have dealt with the same set or the same problem.

Oh, I forgot; I need to find a PDF file with the operator manual for that Hickok Model 532!

[doogie812]

It dose not heart to crank the filament voltage up to 7 or 8 volts overnight. Let it cool down and test it again. In fact if the tube is a little gassy this will help burn off any O2. Andy is very correct. DO NOT rejuvenate the tube at all cost. I would have to see the picture before even thinking about rejuvenating the tube and only with a Beltron quality type tester. I have gone as far as to switch the red and blue cathode leads so I could balance the tube for good B/W. As far as the chassis tubes go. All tubes have a date code. Many web sites exist to help you decode them. Good luck. Doogie

[ctc17]

I have seen several round tubes with one open filament so I would not cook it, I have also seen several of them gone or go to air with normal handling and not to mention the bent shadow masks. I have a set with a super strong crt and horrible cataract and have decided to leave it. The odds of damaging the crt are too great. I am reluctant to even remove the base or move my round sets.
If we were talking a rectangular tubes i would say who cares... but the round ones....handle with care!

[Tubejunke]

Remember that in my original post that I mentioned mainly just questioning the blue gun being slightly weaker than the other two, which are about equal. I am glad to know that I can bump the filament voltage up without worry of having them go open, but I don't think that I will do it overnight. Sorry, I'm with ctc17 there; just too risky! With my luck I would wake up to a no glow situation and that would be really bad. I didn't really ever think that my tube was bad, but if several people chimed in and said that the blue gun being slightly weaker is the first sign of "roundie" death; then I might be a little worried. I'm saving up to get the necessary capacitors that I suspect are causing the HOT to have a red hot plate and smoke from underneath. That way I can follow Doggie's advice and hopefully take a look at the picture. I just hope that there aren't a bunch of other color related issues that will keep me from actually seeing a reasonable color picture. I guess if worse comes to worse I can look at each color individually for brightness in regards to any concerns with the guns. I think they will be fine and just get a little stronger with some use. Call it what you may, but I have seen B&W tubes get much better after several hours of use.

Anyway, I'm just not used to the many issues that come along with a color picture I guess. I used to own a couple of round tube color sets as a kid because they were pretty cheap and reliable. The situation is different trying to resurrect a set that hasn't been used since the late 70s