[Milsurplus] [ARC5] GO-9 Project: Why the Resistor?

[Bob kb8tq]

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

> On Oct 22, 2019, at 3:52 PM, Hubert Miller <Kargo_cult at msn.com> wrote:
> 
> I notice that pains were taken to balance the OSC and PA fils to ground. I would also ask, why is the OSC filament raised above ground ? Is that to isolate, prevent distribution of RF via the filament lines?
> Perhaps some of the OSC ( and PA ? ) balance concern was that 800 Hz fil current would modulate ( to some extent ) the output in A1 mode ? 
> And in the IPA, its effect would be minimal ?
> But why the 9.6 volts is a mystery to me also. That wouldn't I don't think, diminish plate current all that much.
> I would be interested to know the DC resistance of OSC fil chokes L302, L303. But I suppose it's nowhere near 4.5 ohm.
> -Hue
> TNX OM ES 73 DE Dave AB5S<image001.jpg>
> 
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