> If "tinks" in a vacuum can be heard (ie. de-wiskering a vacuum cap), then
> big bangs in a vacuum should also be heard.
>
> Phil
Actually all the banging and tinking you hear from the tube are
conducted through the elements to the envelope and then to the air.
That isn't the bulk of the noise you hear. The bulk of the noise is
caused by other things in the PA moving and arcing when the tube
faults.
Amplifiers get very quiet during a fault if you use enough series R in
the supply, and series R of the correct type, to limit fault currents.
My big amplifier, with an 8000 volt supply and 40 mFd of
capacitance, barely makes a sound when a tube occasionally
faults. That's because it has 25 ohms of six inch long globar style
resistor and a dump circuit. The amp just tics, shuts off, and resets.
The most common cause of a fault is either outgassing or a
whisker (barnacle) in the tube after an extended period of non-use.
If the tube arcs from a parasitic, it will arc from fundamental RF just
as well.
73, Tom W8JI
w8ji@contesting.com
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