CRT test
 

I have a rebuilt (channel master) 23v crt that test great on the green and practially dead on both the red and blue (8v can barely get it above the cut off range indicator on the CR70 and cut off adj is barely there at all. Test poorly on the CR161 as well so I know its not the tester. I can get a strong green raster of course but the blue and red take full G2 and a brightener to make any kind of pic. What I was wondering is it common to have such different readings on guns (two nearly dead and one very strong)? I don't have enough exp to know if this is common.

It seemed to be rather common on certain makes of CRT's. Admiral and Westinghouse, plus Motorola CRT's had this problem most often.
Unfortunately, even with only one gun bad, the CRT, still had to be replaced.
Channel rebuilts, were only slightly better, than the local rebuilder's products.

hook them up full brightness, run for a day or two, increase heater voltage a little, then hit them with a stick near the end of the tube where the red lights are till you hear a spark inside. I did it to xl-100 tubes all the time, only one out of say 20 did not get better.....

we never had any problems with channel master rebuilt tubes.we used them almost exclusively.jack the heater voltage up and let it cook or clean it a few times with your crt tester.they held up very well in my experience

Being far from an expert, to me, this sounds like it would snap off the end of the tube.

are you thinking a weld came loose?

Aside from forgetting to say don't hit hard enough to break the glass squirrly's comment seems plausible.

So I am guessing some "taps" on the end is what was meant.

Most likely. The instruction manuals for some CRT tester/rejuvinators actually instruct the user to tap the neck during some proceedures...

I used to use a screwdriver handle to gently tap the neck while pushing the rejuvenate button on my tester, particularly when there was a short and the "remove short" function on my tester was having a hard time.

When I was in college I use to buy tv trade ins from the rca dealer in town, and sell to the kids in school... Some were the old "mural" tv's rca 17" or so, all tube, with the rocker toggle switch on the front. Then lots and lots of the early xl-100's they use to run so bright, that in a few years the tube was really bad... I did not have a picture tube restoration machine, but I did have a home made dc power supply I made years ago, and still have it... 18V CT transformer from Radio Shack, 3 amps I think.... Made it to be 2 transistor +- 9v somewhat regulated.... With 2 pots to adjust the levels.... Well I used that PS for everything including charging car batteries.... For those xl-100's I use to attach the PS to the heater wires and run the set full brightness full G1's and Full Drives for a few days, with really hot heater voltages.... The tube would snap inside, you could hear it, and see it. It was just like the B&K restorer we had at the tv shop I worked at, When you pushed restore, you could see it spark inside the tube... When you saw a good one, the tube was done... So while running the tube once it was on for a day I would help it snap by hitting it, near the end of the tube, either just at the point where the glass made the radius to the plug, or along the side above the heaters, or first grid, or second grid. After it would snap a few times, turn off the guns that had already snapped, the tube was in much better shape, and I never had a complaint, I kept one to be sure it was a long term fix.... There were no shorts, it was just to boost emissions. It worked on a regular basis, and I would do it today if I had to.... Seems like it was doing somewhat the same as that B&K I had at the tv shop I worked at for a few years.....

You can hit it with what you want, I started with a wood dowel, then moved to a screw driver handle, then went to the point, it really made it sound like the whole tube was ringing inside. I never broke one. How tough is a tube.... Well when I was a kid we had a 21D something giant rca floor model in the basement and it had a broken filament we were not going to fix it, and I talked dad into breaking the tube open to use as a screen for 8mm movie projector. He tied a rope to the end of the neck, and we jerked that entire tv all over the floor and never broke it....

It all depends on how comfortable you feel banging on it...... I would not do it in the cold, or use a hammer, socket handle, or anything with real mass to it, just wack it with a 3" x 3/8" wood dowel, or a small pocket screw driver... Close yer eyes just in case....