Removing Shorts in Picture Tubes and Others

You can also use a 450 V cap 100 mfd or greater to blow the short out of a tube or CRT.

 It generally is a "Do or die" last ditch method but works. Sometimes it requires a few tries.
 I have used it on more than one CRT myself, successfully.
 A cap checker usually limits the current , so it may not always work, as its the current hit along with the voltage that can blow it out.
 Charging a cap with a cap tester is a great idea though.

Hi Cliff, 
That reminds me of a story I heard from Uncle Ed WA3PUN (Silent Key) about a radio transmitter that he had taken to an old time radioman for help to fix. The set was blowing fuses and Ed was perplexed. Much to Ed's surprise and alarm the fellow put in a 20-30 Amp car fuse into the fuse holder. Ed protested. The repairman said don't worry. Then he turned it on. Some smoke then rose up out of the chassis showing where the short was. That was the whole idea to find and locate it! Well, the problem was solved and the radio back into operation and Ed had a good story to tell after that.
73, DeWitt  WB6FBF

I am not into to the field of TVs repairs so I have no experience in that field. But I must say, that's an eye opener to me. A very good explanation that even I could follow.

Very good at your troubleshooting. There is something worth in that, to finding shorts in radios too. I won't forget that trick anytime soon. Thank you!
PS. It does remind me of the issue Transistor whiskers and using that technique (only at a much lower voltage though) to remove that internal short.
Again Well Done, glad you shared that.

Some of us are familiar with CRT testers and have used them to attempt to remove shorts that sometimes would occur in picture tubes. Applying a high voltage momentarily between the offending elements could remove the short. 

While checking out some type 59 (triple grid amplifier) tubes today, I found one that had a mysterious Plate-Screen short. The tube itself looked good. The short was a fairly high resistance one. It could be checked on an Ohm meter (no filament voltage applied) and it measured about 1.5 Meg Ohms. My (2) Hickok tube testers neon short tests had clearly showed it between the Plate and Screen sections.

This particular 59 tube is a rather tall one with long lead wires. I got to examining it after giving the matter some thought. Prior to that I figured I could at least get some use out of it triode connected. Well, I looked the tube over very carefully. Eventually, I decided that the short was probably located below the stem press between the adjoining plate and screen grid wire leads. How to remove it? Not having a CRT tester these days, I decided to try my EICO cap checker's electrolytic leakage test and see what happens. Cranking up the test voltage I got a lot of leakage indication on the neon bulb but no flashes indicating the short location being found and hopefully cleared. The EICO has a fairly high internal resistance on the short tests and that was probably the reason for no "flash".

So I proceeded to a fairly stiff 400 VDC power supply I have which has an on-off switch in the DC output lead. I hooked up some test leads to the screen grid-plate pins on the base of the tube and then briefly switched on the HV. Now I could see the short where a small arc was occurring. It was between the wire leads right below the stem press. A few applications of the HV seemed to remove the short. The tube tester confirmed that the short was now gone. A quality test showed the otherwise good looking tube to be somewhat weak but now could be used as intended. That is as a class A pentode output stage, triode connected class A driver stage or triode connected class B stage. I am mostly interested in the class B use of the tube. I have wanted to build up a modulator using (2) or (4) of these tubes for a while now.

Well, that is my story for now ...

73, Rod  WB6FBF