In the paper "Evaluation of Arc Damage to Power Triode Grid Wires" by
G. Bronner, J. Murray, and J. Sorrentino (Plasma Physics Lab,
Princeton), in Dec 1966 IEEE Trans on Electron Devices, a test setup
was made using thin aluminum foil (0.0008 inch thick) and a source of
high voltage, switched through a vacuum switch. Various circuit
components were installed (R and C) to simulate real power supplies
connected to a tube. The use of a 0.5 uF shunt capacitor for stored
energy, and a series R resulted in a damped ringing at 50 KHz.
Raising the series R to 9 ohms resulted in critical damping. There
was no RF magic and no parasitics - just oscillatory response from
the distributed and lumped L and C of the layout.
It does explain one of the curious things about arcs inside vacuum
tubes, as to "where is the pecker track" or arc damage on the
elements.
Abstract:
Experiments involving aluminum foil damage tests and a simulated grid
structure were performed to relate such tests to the minimum energy
required to damage the grid structure of a type A-15186C (RCA?) tube.
In the case of foil tests conducted in air, it was shown that the
energy in a particular fault is related to the foil hole size and is
in close agreement with engineering calculations and published data.
In a vacuum arc gap the damage is much less than indicated by the air
foil test. The arc becomes mobile and the energy dissipation appears
widespread over the surface area rather than being concentrated or
anchored in a spot. The damage or hole size was much smaller than
obtained from engineering calculations. With energies up to 100
Joules and charges up to 0.25 Coulombs, more than 100 pulses were
required to damage simulated grid wires to the extent where breakage
occurred. On a single shot basis, energies in excess of 3 kJ were
required to produce damage.
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