Rich wrote:
<italic><FontFamily><param>Courier</param>> >Arcs inside the tube do make a
large bang if
the amplifier does not have
> >enough ESR in the anode system.
>
> When a 2000pF vacuum variable arcs, it makes a
barely audible sound.
</italic>What an amazingly poor analogy. A vacuum
variable is generally in
a resonant circuit with very little reserve
energy. When it arcs, the
circuit is detuned and energy flow immediately
stops.
A power grid tube, on the other hand, almost
always connects
across a dc supply with considerable stored
energy and other
components in the path.
When it arcs, it has to pull the supply with its
high stored energy to
ground and does so through may components that
are connected
in series with the path.
When you have some time, do the following
experiment. It may
help you understand the problem.
Charge a 40 mFd capacitor to 4000 volts and
discharge it with a
vacuum relay. Listen to the noise.
Now do the same with the vacuum relay across a
4000 volt
charged 1000 pF vacuum capacitor. Listen to the
noise.
For an added measure of realism, throw a RF
choke in series with
both when doing the test.
You will hear a large difference in noise.
Amazingly enough, no
parasitic oscillation is
required!!!<color><param>0100,0100,0100</param><FontFamily><param>Arial</param>
<nofill>
73, Tom W8JI
w8ji@contesting.com
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