[AMPS] parasitics

[Peter Chadwick]

I question the parasitic bending, because I don't see where the current
comes from. In an oscillation mode, as opposed to an arc, current is limited
by emission, and that's around 65mA per watt of heating current for a
thoriated tungsten filament. This gives an upper limit for the 3-500Z
filament assembly of around 4 to 5 amps. 

Rich suggested that more might be available from depletion of the space
charge: however, I have a problem there in that it doesn't take long to
deplete a space charge - microseconds - and it needs one hell of a lot of
electrons to push up to the levels needed for bending a filament, while
mechanical rigidity and size says that there'll be inertia to be overcome. 

Re Tom's point on neons. My father taught me that in about 1958. I've found
it true, and I can't explain it.  Another indicator is a loop lamp, where at
VHF you get a blue glow in the bulb - I don't know why. As far as
neutralising GG stages is concerned, it seems a good idea to me. And you can
do it cold.

The latter is advisable - I was neut'ing one tx in the lab once when my
finger slipped and I got 2KV. It is not an experience that I reccommend or
wish to repeat!!

On the 6146 variability, I do not agree with Tom that they are on the knee
of the curve. These are DC conditions, and the plate voltage is 750, the
screen at 210, and the bias around negative 45 volts. I'll admit tube
variability is not as bad as transistors (and ICs). Hard experience has
taught me that with RF analogue IC's, second sources usually aren't.

73

Peter G3RZP

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