[Amps] salvaging shorted tubes

[Tony King - W4ZT]

Will Matney wrote:
>>         I would like to see a thread start on trying to salvage shorted 
>> tubes.  My success ratio over the years has been about 1 in five.  Richard 
>> has mentioned a technique of spinning the shorted tube at a high speed in 
>> some sort of a centrifuge.  I have heard other techniques such as 
>> applying 
>> voltage (both AC and DC) across the short.  Some have suggested
>> discharging 
>> large capacitors across the short.  
> 
> 
> Both similar to the way a CRT rejuvenator works. They charge a bank of capacitors and apply it to the CRT elements. I've saved many of a CRT this way, or at least give another years life to one. I still have MY B&K 467 rejuvenator here and keep it handy in case I need it. I've often wondered if it could cure a small short out of a tube. The only problem I thought of though was that the tubes grids could have a gap in them created by the arc thereby stopping so much of them from working at all. That is if the grid only has one connection. I have seen that happen to a few CRT's that were really past saving.
> 
> One Ham I know simply attaches an AC 
>> line cord across the elements and plugs it into the mains.  Apparently
>> this 
>> works, some times.  
> 
> One thing about this method, somethings going to give or move until a breaker kicks, hi hi!
> 
> I have always wanted to try Richard's method but
>> simply 
>> have not done it.  I would like to hear success rates from the various 
>> methods.
> 
> 
> I've heard of some taking a rubber mallet and striking the top of the anode on steel tubes disloging the offending matter and sending it to the bottom of the tube.
> 
>> 73 de K5JV
>>
>> Lon W. Cottingham
>> 1110 Golden Bear Ln.
>> Kingwood, TX 77339
>>
>> 281-358-4207
>> 281-358-4234 FAX
>> 281-795-1335 CELL 
> 
> Best,
> 
> Will
> 
I watched a friend of mine attempt to rejuvenate a few 3-500's. He used 
a Variac (fused) and applied the output between the grid and filament 
with filament voltage applied. There were some intermittent tubes and he 
tapped on the tubes until they sparked inside.  Success rate was 
probably similar to Lon's at about 1 in 5.  One tube in particular, 
cleared of its short, showed a very small white hot spot on the anode at 
idle.  The grid apparently had a small spot blown out of it which 
allowed unrestricted current flow. It was a very enlightening experience!

73, Tony W4ZT