[AMPS] TL-922

[Rich Measures]

>
>I have just pulled the covers off my Sick TL-922 and have found
> the following problems.
>
>1: one of the 3-500's had lost it's vacuum seal due to a fracture of the
>   glass, everything inside the tube was covered with a white film,
>which I under stand is normal when this occurs.
>
... when the filament is lit

>2: The only other component that is visibily damaged is a 220pf silver
>mica cap  at the base of this tube.
>
>No problem, of course to replace the tube or the Capacitor, however am 
wondering
>which event is likely to have occured first. Did the CAP go out and
>cause the fracture of the tube glass  

not likely

>or did the tube blow and cause the 
>cap to explode   ......   or.....and more importantly,  is there something 
else that I have not yet
>discovered that
>might have caused this catastrophic failure ?
>
Failed grid caps are typ. caused by parasites at  c. 130MHz.  Failed 
glass/metal seals are typ. caused by rocking the tube horizontally during 
removal from the socket.  

>I have had this unit for about 14 years now  . am the  original owner
>and have had a few other failures over the years of a different sort..
>LOst tube  ..... fried filament xformer.

When a tube grid/fil. shorts from the aforementioned parasite, the +120v 
power supply is shorted on standby.  The unfused fil. trans. burns out in 
short order due being shorted.  The fix is to remove the +120v connection 
to the bias relay contact so it can't happen again, replace the int. 
shorting tube, and replace the filament trans.  .  [see Circuit 
Improvements for the tl-922 article on my Web site for details]  .  
SB-220s have the same prob.  
>
>I am a bit apprehensive about just replacing the CAP and tube before
>being certain that it won't do a repeat  when I fire it up.

RF Parts allegedly sells a Chinese 3-500Z that has a similar Mu (130) to 
the Eimac variety that is no longer made.  .  
>
> There were no loud bangs before this thing went south  I switched it off
>and found that it  did not fire up when  I next tried to use it.
>The only unusual occurance prior to the failure was an intermittant GRID
> current reading of about 50-75 mils while  the unit was  only idling.
>
It is costly to ignore warnings of impending disaster from the Amplifier 
Fairy Godmother.  

>Any thing else I should look for while I have this unit's  covers off ?
>Any body else encounter a similar problem ?
>........
-  later, Gus

Rich. Measures.  Web site:  www.vcnet.com/measures


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