[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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