On Jul 21, 2006, at 10:11 AM, Peter Chadwick wrote:
> We have a number of possible scenarios:
> 1. We get, for some reason, an arc from plate to grid. The resistor/
> fuse/what have you opens. Because once the arc is struck, it's a
> low impedance with around 50 volts across it, the grid starts to
> hare off towards the plate potential. The arc doesn't immediately
> extinguish because it's got the grid plate capacity to charge. This
> gives the chance for either the grid - cathode to arc, or the grid
> to start pulling lots of current from the cathode because it's
> trying to get to the B+ line, or both. The arc may well extinguish
> once the cathode reaches saturation, since that will try to clamp
> the grid at some lower voltage than the B+, and the grid plate
> spacing may then be enough that the arc can't maintain itself.
> Either way, we may well have a bad tube as well as a fuse or
> resistor to change.
> 2.We get, for some reason, an arc from plate to grid. The resistor/
> fuse/what have you opens. The arc extinguished, teh grid floats.
> Internal plate grid leakge starts pulling the grid positive.
> Depending on the extent, and the drive conditions prior to the arc,
> we can have a variation of scenario 3, where the grid is pulled
> positive by leakage as well as the secondary emission.
>
> 3. We overdrive the grid, and it gets hot, and the resistor/fuse/
> what have you opens. The grid is now floating, is hot and emitting
> electrons, so it goes positive atracting more electrons from the
> cathode, which hit it with kinetic energy so it gets hotter so it
> emits more so it gets more positive so it attracts more
> electrons...........and so on until we have a run away plate
> current situation.
incredible
...
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|