CRTs that are least likely to rejuvenate

[radiotvnut]

When I was about 13 or 14, back around 1990, a TV shop gave me an old blue B&K 465 CRT tester/rejuvenator. Even in 1990, it was highly obsolete and he probably hadn't used it in years. Still, I was happy to get it and it would check older delta-gun color tubes and B&W tubes, which was the majority of what I was getting, at that time. It had three rejuvenate settings and I found out quickly that you'd better be careful, or the tube would be worse than before. I had pretty good luck with rejuvenating the older large-neck B&W tubes. The small-neck tubes, like what was in the 9" and 12" sets, was a hit or a miss. Sometimes, rejuvenation would work and hold up, sometimes it would come up and fall back down, and there were a few times when the tube would get totally wiped out. As far as color tubes, I never had any luck getting a color tube to stay up with that tester.

By the mid '90s, I was seeing more and more sets with inline-gun tubes and the old tester could not handle those with the sockets I had. I later found out that there was an "SP65" socket adapter that would allow the newer sockets to be used with the old tester, but given the crude rejuvenate function of the old tester, I probably needed a better one.

So, I broke down and bought a new B&K 480, about $875 at the time, and it would test virtually any tube that I ran across.

I used the B&K for years and in the very last days of CRT TVs, I found a Sencore CR70 at the flea market for $25. That tester was built better and seemed to be more advanced than the B&K, but the B&K was easier to set up. I used the Sencore for a while, until it developed a problem that I've never fixed.

Currently, I still have my old B&K 480, a couple of 470s, one or two 467s (the one with 3 meters), a 466, and a 465 (all in various states of disrepair at the moment). I have the Sencore CR70 that has issues, and I have a mid '70s RCA tester.

Even with later model testers, there were still some tubes that I just didn't have very good luck with. These tubes include:

1. '90s Zenith color tubes, especially the 25" and 27" tubes. Those tubes were garbage to begin with and it's hard to get anything good out of something that was garbage to start with. Those tubes would prematurely get weak and/or intermittently short/arc. When they shorted, they blew up other parts (usually, the power supply and/or video driver circuitry).

2. Late '70s-early '80s Zenith inline tri-focus tubes, especially the 23" and 25" tubes. When they were strong, they looked great, but when they got weak, there was not much you could do. At best, rejuvenating them might help a little, but they never bounced back fully and they'd never stay up long. The 13", 17", and 19" versions seemed to last longer.

3. Sony Trinitron tubes. If rejuvenating them didn't blow up the tube, they'd often look good for a short period. Then, they'd fall back down and look worse than they did before you rejuvenated them.

4. The 12", and smaller, B&W tubes with the small neck. I've had luck with a few of those, but I've had more of them that either wouldn't come up at all or they'd fall back down in short order.

5. In the late '70s-early '80s, RCA had some crap delta-gun tubes that would short and/or lose emission, and they wouldn't take a hit very well. The older RCA jugs would take a hit and keep right on going.

6. The 25V Sylvania black-face delta-gun tubes. They produced a great picture but didn't last long and usually would not take a hit.

It should be noted that rejuvenation should not be considered a permanent fix. Some tubes will hold up longer than others, but rejuvenation was mainly meant to buy the customer some time, while a replacement tube could be sourced, or the customer prepared to buy a new TV. In today's world, it's not as simply as ordering a new tube and rejuvenation is often all that can be done to save an old TV.

[dishdude]

Sony and 1993-1995 Zenith are by far the worst.

[Electronic M]

I've learned that the rejuvenate button on my B&K 466 is only for tubes that I want to "kill or cure" everything else that's mediocre I first will cook for 15-60 minutes at normal settings, then for up to a day at 1.4x normal heater voltage, then if still unusable go to rejuvenate.

If a tube is a little weak a brightener is usually a safer bet than a rejuvenation. Most tubes that a brightener can help will live long enough to source a spare and then some.

[JohnCT]

Originally Posted by radiotvnut

It should be noted that rejuvenation should not be considered a permanent fix.

Indeed, it is a last resort procedure. Some guys will buy one and use the "clean"function as if was sort of helpful maintenance like an oil change.

With regards to CRT testers, I have four B&K 467s, and one of them I modified many years ago after reading Sencore's sales pitch outlining what was wrong with B&Ks testers in the way they cut off the heater voltage during rejuvenation. I know it was ad-copy but it made sense from what I observed using the B&K.

One thing I noticed about using the B&K is that it was often tough on the tube. When using the clean or restore, it would apply the current to the cathode while simultaneously removing the heater voltage. The meter would show the current though the cathode while the button was held down, but if the tube held the current for too long and the heater went cold, there would be a violent jerking and swing of the meter accompanied by visible arcing in the gun assy. This often happened so fast you couldn't release the button fast enough.

What I did was take my 467 apart and jump out the switch so the heater voltage stayed on during the rejuvenation. When I pushed the rejuv button, I would keep my other hand on the heater adjust button and slowly lower the heater while I watched the meter. Ideally, you want the meter to slowly reduce, but when I noticed the meter start to twitch, I'd raise the heater voltage back up until the meter stabilized. I'd then start dropping the heater voltage again until the meter moved smoothly to about 1/4 range then I'd let off the rejuv button.

That procedure seemed to be a lot easier on the cathode and I had a lot more success that way. I never used the Sencore but I think they had the right idea.

John

[vol.2]

Originally Posted by Electronic M

I first will cook for 15-60 minutes at normal settings, then for up to a day at 1.4x normal heater voltage, then if still unusable go to rejuvenate.

What do you mean "cook?"

[Electronic M]

Originally Posted by vol.2

What do you mean "cook?"

So CRTs have this thing in them called a getter that is made of highly reactive metals that soaks up gas molecules. The cathode that makes the electron beam is also made of highly reactive metals, so when the CRT isn't run for a prolonged period and starts to act like a getter and react with gas forming insulative oxides on the cathode that block emissions. When you run the tube you boil those gas molecules off the cathode...The longer you cook the cathode at normal or slightly elevated heater voltage while drawing test or operating cathode current the larger the percentage of the accumulated gas leaves. The tubes emissions will wake up as it cooks.

[vol.2]

Originally Posted by Electronic M

So CRTs have this thing in them called a getter that is made of highly reactive metals that soaks up gas molecules. The cathode that makes the electron beam is also made of highly reactive metals, so when the CRT isn't run for a prolonged period and starts to act like a getter and react with gas forming insulative oxides on the cathode that block emissions. When you run the tube you boil those gas molecules off the cathode...The longer you cook the cathode at normal or slightly elevated heater voltage while drawing test or operating cathode current the larger the percentage of the accumulated gas leaves. The tubes emissions will wake up as it cooks.

Okay. Thanks for the explanation. To clarify, when you say "while drawing test or operating cathode current," do you mean that you leave the CRT tester on one of the settings (if so, which setting?) while simultaneously raising the filament voltage?

Thing is, I have a CR70, not one of the B&K units, so I'm not sure what the exact analog of your suggested procedure would be. I can set the filament voltage higher and let it sit there, but I'm not sure how I would "drawing test or operating cathode current."

[DavGoodlin]

100% no good on anything with inline guns, including all Sony. The early 70s RCA one-gun 17" tubes did seem to respond better though.

I too have been very disappointed with soft-looking Sylvania replacement CRTs which won't wake up, I expected much more from them.

Recently, I repaired a Beltron and those are easier on rejuvenation than most. I have been my Heathkit IT-5230 for 45 years, which is very similar to a Beltron but with improvements. The rej/cln uses AC to remove polarized cathode glaze, the DC is for rejuvenating.

The first one I used was at VoTech shop in 10th grade. They had a Heathkit that I used on an RCA CTC16XL that had completely lost red. The results were so impressive, I bought and built one.

I later worked at four different TV shops and none believed in using one for these valid reasons stated in previous posts, we were selling may CRT installs then.

My own experiences ALL that I have to go by. I also have a BK 445 that is a great tester but I only push the button if the H-K will not bring it up.
The B&K WILL destroy a cathode with is capacitive discharge method.

You have to try hard with the H-K but it is possible if you're not being gentle. What it does is place 300 VDC across cathode and grid, while you vary filament, both gun current and ballast lamp brightness will let you know how heavy you lean on it. Releasing a button of lights flash on.

[vol.2]

Originally Posted by DavGoodlin

100% no good on anything with inline guns, including all Sony.

Is that true for all of the restore functions, or just the rejuve? The auto restore function of the CR70 seems to indicate that it is operating the guns with an elevated amount of current and higher than normal filament voltage, but at a normal voltage level. This is very different from the rejuve function which seems to just whack it with a bit hit of volts.

[ARC Tech-109]

I have both the B&K 466 band 467 and found the clean/balance and rejuvenate-1 functions to be much easier on the cathodes than the hard rejuvenate function which I believe just strips the cathode face away. I also reduced the size of the capacitors that are thrown across during the clean/balance on my 467 and a "lighter" light bulb ballast on the 466. As JohnCT pointed out the 467 cuts off the heater during the rejuvenate cycle and this causes them to arc heavily during the last of the heat basically destroying the face IMO, as a retired radio tech the rule was to make sure cathodes were fully heated before applying scree/plate and drawing current to avoid damage and this feature of the 467 seems to do just the opposite. Mine are modified to keep the heat on.

Tubes we can add to the list that should never be hit with a rejuvenator are the little 4" and 5" Trinitron tubes used in the BVM-5300 or KV4000 & KV5000 series sets and 90's vintage HP test equipment that use the individual fast heaters as prime emitters, the heaters themselves only pull some 40 MA each and a zap from a rejuvenator will open them... speaking from first hand experience. These tubes do have a problem with K/G1 shorting on the red from the whiskers and my solution is to run the heater at rated voltage and drop no larger than a 0.47uf cap charged to 150V across them cathode negative to pop the whisker open.

Just for the record I've had rejuvenated delta guns last a decade or more after a "dusting" with the clean/balance function and many CRT based computer monitors run 24/7 until something on the board died after a visit from my 466. I've also had Japanese delta guns die withing just a few months of a clean/balance so really it's a gamble either way. I hit the gun of my Motorola R2670 green screen with the rejuvenate-1 of my 466 almost 20 years ago and it's still going strong averaging 8-10hrs of use daily.

As the old disclaimer goes... your mileage may vary.

Retired Radio Tech-109