>Rich Measures wrote:
>>
>>>Back to the original question, then: exactly what produced the
>>>mechanical force that made the filaments move?
>>>
>>This is still somewhat puzzling to me Ian. The peak grid current during
>>the 110MHz oscillation is sufficient to melt the copper wire in the grid
>>RFC.
>
>I'm still using the neutral term "during the event".
>
>> . According to the fusing current ratings of copper wire, the
>>current (and the resulting electromagnetic force) must be substantial.
>>The tungsten wire is fairly hot. Apparently, the electromagnetic force
>>is strong enough to bend the hot wire.
>>
>
>Now can you take it down to the next level of detail, please:
>what currents flow in which wires, in which directions, and how do they
>produce the force that bends the wires?
IMO, the DC current in question issues from the cathode, flows through
the grid, and returns to the HV supply through the chassis and the grid
current meter shunt resistor.
>Bear in mind that a valid explanation has to cover all three of the
>following points:
>1. According to the photographs, it's the heater wire that moves, not
>the grid.
Yes, the hot (1820 degrees K) tungsten wire bends during the event. The
grid does not.
>2. Currents in wires can produce their own magnetic field, ... ...
Can? Current in a wire ALWAYS produces a magnetic force at a 90 degree
angle to current flow. However, in this case the force angle is a bit
sticky wicket due to the 45 degree winding pitch of the double
helix/helices.
>...but you have
>to consider ALL the relevant wires.
>
>3. RF current cannot bend the wire.. - above a few kHz it's too fast for
>the wire to follow. To produce a net physical movement there has to be a
>net DC component (or a low-frequency transient).
I agree, it's DC.
>Sorry, I don't know what the right answer is - only the conditions that
>it must meet.
>
If you lived a bit closer, Ian, I have three, intact, filament/grid
shorted 3-500Zs that we could disassemble and inspect. My best guess is
that we would find bent filament helices in three of them. IMO, Mr.
Rauch's intermittent, disappearing gas theory does not explain the
evidence. The idea that such an event happened at the same instant in a
pair of virtually-new 3-500Zs is hard to believe.
Rich---
R. L. Measures, 805-386-3734, AG6K
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