I thought it would be a good idea to combine all the tips and tricks on CRT rejuvination. Here's what I've picked up:


When testing a CRT that's been sitting around for long (years or decades), leave it running for a few hours to wake it up. Using a slightly elevated filament voltage of 8 volts or so can help. Don't rush to rejuvinate it.


If a CRT really is weak, try to get your hands on a modern CRT restorer like a Sencore CR70. Older units like the B&K 440 are pretty rough on the filament. Basically, they just charge up a capacitor and discharge through the cathode. A better unit will use a more controlled method.


Use the lowest rejuvination mode first and re-test. Only go up to higher settings as a last resort. Each time you try to rejuv. a tube you are blowing off a little more cathode material. Too many attempts and you've got a dead tube.


CRT brighteners boost the filament voltage and although they help for a while actually accelerate the demise of your CRT.


It's a good idea to add a current limiter (e.g. CL-90) to a series wired set to protected the CRT from startup current surges. If you have the room, adding a separate 6.3VAC transformer for the CRT filament works well too. Just remember to replace it with a 10 ohm 10 W resistor in the series string.


If you have an open cathode (good filament but no emission) you can try this technique I got from jeyurkon. It worked fine with my Sencore CR70.


This is from the Sencore CR31A SuperMack manual, so I don't know if it works with all rejuvenators.

If a CRT indicates absolutely no emission, and the filament is still working, an open cathode is indicated. When this occurs the automatic controlled REMOVE G1 SHORTS circuite of the CR31 can be used in an attempt to weld the cathode. (goes on to talk about resoldering the pins first).

1. Set the BEAM BUILDER function switch to the REJUV 2 position and allow the filament to warm up for 60 seconds.

2. Set the Function switch to the REMOVE G1 SHORTS position and IMMEDIATELY press the REJUVENATE OR RESTORE button before the filament has time to cool. At the same time, tap the neck of the CRT.

3. If a flash occurs in the CRT neck, release the REJUVENTATE OR RESTORE button. Return to the CRT TEST section and check the CRT for emission. If no flash occurs and/or no emission can be read on the meter, the cathode cannot be welded to restore performance.


John

I'm sure you guys can add more to this thread :)

One I'd like to add:

Never Rejuvenate/Clean and Balance/Restore a CRT with it's face down. All the junk that's blasted travels down through the gun(s) and can short the CRT elements. With the neck parallel to the ground, the junk usually falls to the bottom of the neck and harmlessly away from the gun(s). I've had this painfully ($$) demonstrated on a customer's CRT...


Also, if you are using a B&K 4XX series checker, don't use while your bare knee is in touch with the ground. Shocked the %*!& outta me when I was a teenager and checking some CRT's for a friend. He had about 30 B/W CRTs spread out on a blanket in his back yard and I went about testing each one - I got to one and got between the checker frame and the bare ground - ouch! Worms came up outta the ground.....

Cheers,

When I was in college I use to get trade in tv's from the rca dealer in town. I fixed them and sold them to students for about $40. He would let me have sets he didn't want for $10. each. The XL-100's usually had bad or low emission tubes. I use to get the 17" or so Mural RCA's with the toggle power switch on it, they were good sets tubes aged gracefully. Well the XL-100's that had bad emissions I use to put a variable power supply across the filiment turn up all the guns and brightness to the max make the tube as bright as possible and then crank up the filiment. After about one or two hours I would whack the neck of the tube with a screw driver until I herd a sharp crack and a nice spark jump inside the tube a few times. The tube would brighten up nicely and when I returned all the settings to normal, and rewire the filiment I ended up with a nice working tube. I did dozens of these tubes like that and naturally never really hit them that hard, never had one break. If I had only one gun giving me trouble I would just turn that gun's drive up and still whack the thing good. This was my last ditch effort at the time, since my investment was not large I really didn't have much to lose. If anyone wants me to give it a try on your roundies after Scotty retires just send me a note........ : )

back in the shop days,we would "wrap"a crt.cut one filament wire and add a section that we had wrapped around the flyback.1 or 2 wraps usually would increase voltage.let the set play for 30-45 minutes.if the crt brightened during the process,then great!some tubes took longer and some required more wraps.in my over zealous youth,i wrapped some too many times.the picture was good for a day or so,then,suddenly,lights out.i learned to be more cautious in my old age!

Don't forget to tap the neck to try to clear any shorts that pop up on the tester...

What a lost art this is. I wonder what the crt engineers thought of testing/rejuvination and all the black magic that goes with it...

Here's a video I made showing how to reweld an open cathode using a Sencore CR-70 https://youtu.be/E3E8EDMZ8aI?t=20m23s

that's a great video Bob!!

Thanks for the post, I am working on the same set you posted on You tube, Admiral 14YP3B with a 10ABP4. It tested dead :tears: I tried your fix, took 5 tries before it took.
Now I have a bright picture, life test showed good.:banana:
Thanks again.

Carl

That's awesome! I'm so glad it worked for you :thmbsp:

This thread needs sticky status.

Don't forget to tap the neck to try to clear any shorts that pop up on the tester...

What a lost art this is. I wonder what the crt engineers thought of testing/rejuvination and all the black magic that goes with it...

We did that. One of those nothin to loose deals, often worked good.

Along with adding a winding to a flyback supplied filament
there is also usually a low ohm resistor in series with the
filament, jump it out. IMHO also last resort but effective !

Sears / Sanyos with Sylvania CRT's that H-K short.
Anyone remember the mod ???
IIRC get the filament above ground, add a 1.5 meg from the
filament to the shorting gun. Also add a .001 cap to ?
Saved a crap load of sets, also worked on others.

73 Zeno:smoke:

any tricks out there to revive a 7jp4..... maybe put it in front of a crystal ball and do a rain dance, lol...

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