[Milsurplus] [ARC5] GO-9 Project: Why the Resistor?
Bob kb8tq
kb8tq at n1k.org
Tue Oct 22 16:44:07 EDT 2019
Hi
Sure, the bigger the cathode, the more “C” there’s going to be. Also in a high
power tube the design probably is optimized for things other than the capacitance
changing by a couple of pf.
Bob
> On Oct 22, 2019, at 4:35 PM, Hubert Miller <Kargo_cult at msn.com> wrote:
>
> Thank you.
> So I surmise this is a greater effect in larger tubes?
> Also that this capacitance could vary with variable filament heating, such as filament voltage change?
> -Hue
>
> >Hi
>
> The oscillator filament is raised off ground because the filament to cathode capacitance would show up
> across C305. C305 is “inside” the oscillator loop. Stray across it will tune the VFO and introduce drift.
> Depending on how the tube is made ( manufacturer to manufacturer) this probably varies a bit.
>
> Bob
>
>
>
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