[AMPS] Big Bang Theories?

[Jon Ogden]

>I know one thing, it sure as heck went BANG!!!
>here, and it wasn't any normal parasitic I have ever seen. I have had
>amps go into oscillation before from weird tuning etc., but all they
>ever did was peg the plate current until I moved the tuning off the bad
>spot. Never have I had an amp in oscillation go BANG!!!.

And I don't think a parasitic oscillation every does go BANG!  Stable 
amplifiers do not just suddenly break into an oscillation.  

> So what do you
>all think at this time? Would welcome comments from others who have had
>this problem. I'm giving serious thought to buying a set of retrofit vhf
>suppressors unless someone can think of a better idea.

Don't mess with the suppressors other than to check the value of the 
resistors.  If they are bad, replace them.  But I would not add the 
nichrome ones.  They may help in some extreme cases, but even in my 
4-1000 amp, they did not make a bad layout stable.

What you likely had happen was an internal arc-over inside the tube.  
Some of the gas molecules inside the plates worked their way to the 
surface of the plates and were released into the envelope.  The bang 
sound you heard was likely these gases burning up.

If this "event" was one of the so-called destructive parasites, it would 
have taken out a bunch of stuff in your amp.  It didn't.  It was a bang, 
most if not all amps bang once in a while.  If your suppressor resistors 
check out, then I wouldn't worry about anything if it still works.  If it 
keeps banging then we may have some other sort of problem.

>At least if I do
>that, and it does it again, I'll know it wasn't the suppressors fault.
>These retrofit ones are the "nichrome wire versions" to get a lower Q of
>the resonant vhf circuit between the tube and tune cap. I checked mine
>with a grid dip meter, and seemd to have a pretty good dip at about 130
>or so mhz. So seemed fairly hi Q I guess. 

You can tell nothing about the Q of a circuit from a dip meter other than 
a relative measurement.  Just cause you have a steep dip is not a 
guarantee that the Q is high.  It means you do have a resonance there.  
But dip depth is dependent upon a lot of things: where you hold the 
meter, how close you hold the meter, etc.  A dip meter is good to check 
the relative dip sizes between different circuit configurations but to 
make the jump that a good dip means high Q is too much of a leap for me.  
It *may* mean high Q or it may not.  When I had AG6K's suppressors in my 
amp, I still had a good dip at my resonant frequency. So they aren't a 
cure-all.  I think they may help in some extreme cases, but for most 
amps, I have difficulty believing that most amps are inherently unstable 
without them.

73,

Jon
KE9NA

--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!


Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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