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 Post subject: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 4:55 am 
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Have a brass based 01a tube that has continuity between the filament pins and one other pin according to ohm meter. Is this tube a display tube in this condition?


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 5:04 am 
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It makes me wonder if one could charge up a fat-old capacitor, say 20,000uF at a lowish voltage of say, <12v and discharge it across the shorted pins. I imagine this would result in one of two things. It would either blow the short clear, or blow one of the internal connections leading up to the short. I suppose one could sort of sneak up on it, starting off with only a fairly low discharge and work upwards hoping the short blows before the internal connection. Hmmm. Yes. Makes me wonder, it does...

- Scott


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 5:31 am 
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this may apply, keep it for reference


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 5:41 am 
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If the short is due to the tube having been dropped, try proverbially dropping it on the other side. Inspect the misalignment of the elements and bump the tube against your palm in a manner that may straighten the elements. Start with a soft bump and If inadequate to straighten the elements, try again harder. You have nothing to loose. I have removed shorts due to element misalignment from being dropped in several tubes. This will only work for larger, older tubes.

Norman

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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 10:44 am 
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Location: Powell River BC Canada
A story from a broadcast engineer. Some expensive British image orthicons
were showing element shorts. I believe they were called 'leadicons'.

When the factory rep arrived, he whacked the tube at a certain place. It fixed it.

The story goes, that some present almost fainted. :D

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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 3:19 pm 
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Let me just say that I "Had" a Mullard 5AR4/GZ34 that was shorted, one element to the cathode. I tried the "zap" method. It managed to open completely the connection to the cathode (you could see it). So, that was the second Mullard 5AR4/GZ34 that I threw into the can (yes, it made noise, it was bad). I still have a metal base Mullard 5AR4/GZ34 with one side open in one of my tube caddies. That one will NOT go into the bucket, I guess I could use it as a half-wave rectifier?

But in all seriousness, what do you have to loose?

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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 4:18 pm 
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Location: 66952, USA
The getter is preventing me from fully inspecting the tube - but I guess I'll try the whack method. Wonder what would be the best side to hit? I need to check again as to what pin the filament shorted against. It is a nice tipped BB rainbow tube. Has value even as a dud.


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 4:39 pm 
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Need to inspect the interior of the tube more carefully.

Light the filament using clip leads and 6 vac and examine the structure in a dark room. Try to light the filament via the short too. Look down the interior and the press area. If the short can be seen and the structure seems canted to one side then smacking the tube envelope into one's open palm may bend the structure enough to clear the short.

Remove rings from hands. These could contact the glass and cause it to break. Wear light cotton work gloves, It is the sudden stop in the palm and the continued deceleration of the elements that will cause the bend. Orient carefully so the bend axis is is in the same direction as the tube as it stops against the palm. It may take one or more smacks for it to happen or not so go gentile at first.

The weak element structure is one of the reasons the "S" bulb was abandoned...

Caveat!
- There may be a short in the base, overflowed solder from a base pin, that is removable with great care.
- There could be severe flashing from the getter pellet onto the press, not fixable...

GL

Chas


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Sun 19, 2017 5:20 pm 
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HOORAY - I think I cleared it but need to test. Here is my technique:

Clip ohm meter leads to filament pin (any) and pin shorted to - in my case grid.

I smacked the tube against cement floor that has a thin indoor outdoor type carpet over it. Need to use judgment as to how hard to smack. I wanted to have a slight "bouncing" effect with the tube. I would advise wearing gloves and eye protection - just in case

I kept doing this rotating the tube as I went, watching the ohm meter needle. I noticed with each rotation a better response with needle. (moved closer to zero)


Stopped when ohm meter jumped to no reading - check filament continuity to ensure still that was still good.

So now I have to test it. :D


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Tue 21, 2017 3:39 pm 
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Only catch is, maybe the filiment shifts slightly when it is heated? Shifts the wrong way...


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Tue 21, 2017 5:11 pm 
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Shorts in tubes with closely spaced electrodes are often due to debris getting trapped between them. Sometimes a well placed whack can knock the debris out and then the tube is okay again.

Problem is, an 01A does not have close spaced electrodes (relatively speaking) and if there's anything inside big enough to cause a short, it is likely to be a broken piece of grid or filament wire or a piece of oxide coating from the filament. Don't mean to sound discouraging but if the tube was hit hard enough to bend the grid into the filament, or run until the filament sagged into the grid, dropping it on the rug until the short goes away may mean that you now only have half a grid or the filament will promptly burn out the next time you power it up. These tubes are around 93 or 94 years old at this point; you shouldn't expect miracles.

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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Thu 23, 2017 10:15 am 
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Location: Cedar Rapids, Iowa, USA
I have found several tubes of Canadian or European manufacture have comparatively soft and weak internal support structures, resulting in the tilting of elements during shipping. They have responded rather well to Norman's whack method of realignment. I don't remember any success with U.S. made tubes.


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Thu 23, 2017 4:31 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Early '22-'24 tubes are poorly constructed, often elements are not accurately centered and any impact to the tube can bend them to short.

It is always worth a try to smack them in the palm of a gloved hand. A trick shown to me by an old time years ago.

GL

Chas


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Thu 23, 2017 4:39 pm 
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Fixed an old 3" CRT with the whack method once. I was fortunate in that it was apparent someone had set the 'scope down too hard too many times, so it was easy to turn the unit over and give it a few good jolts (with other tubes removed, or course).


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Thu 23, 2017 5:14 pm 
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The whack method often works on older "S" (globe) type tubes. Tubes like UX201A etc. These tubes don't have good element support like later "ST" shaped tubes. Sometimes you will see the internal elements at an angle.

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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Tue 28, 2017 12:20 pm 
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I have looked inside older shorted tubes, such as simple triodes, to see where the problem seemed to be, then, held the tube in one hand and slapped it into the other backhanded to jar it, and give enough cushion so it would not break (or use thick gloves to protect against any breaking glass). It worked.
Dont think this is as easy, or possible, with newer tubes.
Mark Oppat


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 Post subject: Re: Any Way To "fix" a Shorted Tube?
PostPosted: Nov Thu 30, 2017 4:22 am 
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i used to blow out shorts in CRT's with an electrolytic of about 40 mfd. Charge up with the TV sets power supply and zap it across the short- normally it was a H-K or screen short. Worked about 50% of the time, and nothing lost if it didn't work. If it worked, then I made money from the repair. Never had a call back either. If you use too big a 'lytic, you can vaporize elements in the tube.
Sometimes you could also weld a broken element this way, by hooking up the cap and then tapping the CRT to jar the elements into contacting position. The spark in the tube was the tell tale it worked about 85% of the time. Sometimes it took a couple of tries.

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