On Nov 2, 2006, at 6:58 AM, ad4hk2004 wrote:
Z is slick... The bench test with just the filament heated fills the
tube with an electron cloud... The electrons have velocity... Some
will impact the grid and be captured... The grid will become more
negative and the excess electrons will flow from the grid to any less
negative point...
True enough, Denny
Z. I did the same experiment when I was in college. Zeb's problem is that he is the person who said:
#643
Re: SB-220 Questions
"With 3.5kV applied, a
good tube in one socket, and +3-5V on the cathode with no RF drive,
you should have about 20mA grid current in the normal direction."
- Z
-------------------------
With +3 to +5 volts on the cathode, "about 20mA" does not flow. Zero grid current flows because the grid potential looks negative with respect to the cathode. .
Consider, that although we view the
filament/cathode to be negative it has electrons departing under
thermal acceleration which makes the filament structure itself less
negative...
I don't have the time at the moment but I will do a bench check on
some 4CX1000's that just happen to be hanging around under the bench
at the moment... I suspect that each individual element in the tube
will show voltage/current under Z's conditions..
With 3 to 5 volts negative on the grid, there should be "about 20mA" of grid current if Z is correct in this matter.
cheers
denny / k8do
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