Hi Jon,
> >> Boy now thats a parasitic I wouldnt mind having, all the
> >> parasitics that I have seen , most of them around the
> >> 4-1000 amplifiers, cause damage to say the least. When
> >> the amp takes off uncontrollably and meters bend around
> >> the pegs, resistors blow, safety trips explode, that what
> >> I call damage.
> >
> >Sounds like you have confused outgassing or gas ingress, a fairly
> >common occurrence, with a parasitic.
> >
> >High vacuum arcs are common in tubes, especially old used glass
> >tubes.
> >
> >I guess if we don't know what a problem is, it's easy to call it a
> >"parasitic".
>
> I disagree, Tom. While some parasitic oscillations in amplifiers are well
> behaved, some are not. In my 4-1000A, for the longest time while building
> it I had a slight oscillation that I could produce every time I brought
> the tune C to minimum. No bangs, arcs, etc.
Same in amps here. When I make them oscillate, they generate
trash and draw current. No bangs, no arcs, no bent tubes, etc.
> However, at one point I was dealing with a cavity resonance. The amp was
> stable w/o the cover. Once I put the cover on, I got a big bang and it
> wasn't from any gassing. However, these sort of events are typically due
> to some other problem such as a bad layout (the orignal problem in my amp)
> or some other failure. I would venture in a "normally" working amp that
> big bang parasitics don't occur.
Ahh. But that was likely a fundamental oscillation, or a low order
mode oscillation supported by the cavity. I can make an amp
"explode" by making it arc on or near the fundamental. I can wipe
out a bandswitch with a HF oscillation, or with excessive drive for
the amount of loading used.
Everyone (except Rich) knows that happens.
Oscillations are no different than intentionally driven signals. All
components follow the same rules.
> And to comment on the point that Rich has said he's never seen arcing from
> a badly loaded amp: All I can say is BEEN THERE! DONE THAT! I've had
> mine mistuned once or twice and heard some real nice arcing. And I have a
> load C with rather large plate spacing.
Jim Baker never knew a thief who took advantage of people's
ignorance, and Rich has never seen a mistuned amp or an amp
suddenly operated with a bad load arc.
What amazes me is how some people swallow his wild claims. PT
Barnum was right.
73, Tom W8JI
w8ji@contesting.com
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