Need advice - would you Rejuv a working CRT?

My Zenith Porthole "Cinderella" plays but it does not have the brightness
of the Raytheon Porthole I just restored where I rejuvenated its dead CRT.
The Zenith uses a 16EP4 and the Raytheon uses a 16AP4.

My Zenith Porthole shows a decent picture in a dimly lit room but I
was wondering if I could get some improvement by Rejuvenating it
with my Sencore CR70. I don't want to nuke my 16EP4 - so I'm
asking for opinions before doing this. What do you guys suggest?

Carl

Hard to answer with out actually seeing the picture myself. Does it go silver at high brightnrss levels or simply wash out? Does the CRT checker show a decent reading? Having worked for the company that invented the process I've brought back many CRTs but there is always a risk.

Maybe, but, I'd be nervous. There is no other sub for the rare 16EP4.
Bill Cahill

Simply put..... NO NA NA NO NO NO NO!! if it is useable as is use it. Even the best rejuvenating equipment can ruin. A good crt.

I consider rejuvenation an absolute last resort, used on a CRT that really isn't watchable at all. It does not always make an improvement, and may make the CRT even worse.

Have you tried using a brightener? They slightly increase the filament voltage, and also have their pros and cons. You might be able to do a rough test with your CR70. Measure emission at normal filament voltage, then increase the voltage a bit and see if emission noticeably improves.

Phil Nelson

On more common tubes, I rejuvenate with no qualms. I am often very pleasantly surprised at the results. In some cases, no improvement is seen, but such tubes are basically dead anyway. On a relatively rare tube, I'd certainly try a brightened first.

Exactly. Rejuvenation should never be the first step if emission can be improved by slightly raising the filament voltage.

I would try a brightener on this particular tube just for a few minutes, and see whether or not you think there is enough improvement to leave it on.

If you do plan to rejuvenate, I would make sure to have another good 16EP4 on hand to replace it with someday. It's usually possible to modify the Zeniths that take a 16EP4 to work with a 16GP4.

I would never do a rejuvenate on a usable CRT, but many better testers have a lower power rejuvenate mode (call "clean" on my Beltron). It works by running it with increased heater voltage while passing a larger than normal current through the cathode (but much less current than rejuvenate). It's a relatively gentle process that limits the current to about 10mA for a few seconds.

I've found that it works very well on CRTs that are usable, but soft looking. It makes blurry low focus voltage color CRTs look like new, and greatly improves CRTs that are slow to warm up.

Here is a video of my Zenith Porthole TV playing:
http://www.youtube.com/watch?v=Lihm3aRpjFg
Maybe I ought to just leave well enough alone.



I have two Zenith portholes - one 16" and one 19".
The 19" porthole (19AP4) on the right has a more yellowish tinge to it.
Does this signify anything good or bad?

The 19" takes several minutes before the picture fully brightens.

Then compare it with my Raytheon porthole that originally had
a brightner on its 16AP4. It first tested stone dead but came
back to life after rejuvenating using my Sencore CR-70:

Now no more brightner.
I think the Raytheon looks better and has more brightness but
I feel the focus is a little amiss.

Only the 19AP4 takes a long time for the picture to get to full
viewing brightness.

Like you guys stated, I was leary about rejuvenating a working
CRT until I got your opinions.


Carl

The different color just means it has a different type of phosphor, or tinted glass. I wouldn't risk a rejuv just because it's slow to warm up, but if you buy, or borrow something that can do a cleaning it might be worth it. I've never had it make things worse. If it's too weak to get any cathode current flowing at the voltage it uses in cleaning mode, it just doesn't do anything. Still, with the lack of a way to get it rebuilt, I would be inclined to wait until it's unwatchable before doing anything. I've had slow warm up CRTs that continued working for years with an excellent picture.

Leave 'em alone.. Sure, a little weak, but, not bad, raally.
Leave 'em alone.
The 19" will need a brightenner, but, not quite yet.
Bill Cahill

I wouldn't rejuvenate one if it was still watchable but if it's getting to the point you describe I might.
I would try a brightener first, if that improves the picture then at least you know the CRT is causing the problem. I really think a brightener might provide a longer lasting solution than rejuvenation, which in my experience is a very temporary solution.

A cleaning with a Beltron machine or similar may be of some help but I wouldn't even think of hitting it with a blast rejuvenation from one of the old style testers.

Would you consider the Sencore CR70 to be one of the safer rejuvenators?

Carl

Not personally. They all rejuv. the same way.
Bill Cahill

Hi Carl;

You probably have already done this, but just in case, check the circuits that feed the CRT- high voltage, video, etc. Make sure the voltages are correct and things like paper capaciters are repalced. A low value of CRT high voltage will afffect the brightness to a large extent.

-Dennis

I have a HV probe that I can attach to my multimeter.
Do you specifically mean to measure the HV on the Anode?

Carl

I do consider the CR-70 to be a fairly safe rejuvenator. Many of the very common CRT tester/rejuvenators are completely manual, so the amount of rejuvenation is completely up to the user. Since most new users are not experienced, you have no idea of what "a little" or "a lot" of rejuvenation is. The CR-70 has quite a few automatic functions. If you let it do its thing, you know whether it has applied "light" or "heavy" rejuvenation.

Overall, I find the comments here on the conservative side. There is a tendency in threads like this to pile on with ever more cautionary comments, to see who can sound the most cautious. You've seen with your own eyes how much rejuvenation helped your Raytheon set.

CRTs that are on their last legs are not incredibly valuable. Unrestored sets are quite plentiful out there, and are the best source for replacement CRTs.

I'm no expert by any means but if it were mine and I tried to rejuvenate it and ruined it instead I would be sick to no end. It ain't exactly broke so don't fix it IMHO!

Focus issues are one common side effect I have often seen with rejuvenated CRTs. Not the end of the world, and still better (in my cases) than the near-dead tubes I started with.

The 21" tube on my Philco Miss America also takes about five minutes to become watchable. It had a brightener when purchased, so I assume it's simply on its last legs. I took off the brightener, since the picture's not dramatically different either way, and I figure it may just die a little sooner with the brightener.

Phil Nelson