[replying to myself, as I realized I had made a mistake] > In the diagram where I isolated the filament, I had to add a connection to > the anode supply to get it to work: > > http://www.vitriol.com/images/tech/vfdps1.gif > > The connection is the one with the ground symbol hanging off of it.
I've replaced that diagram, as I realized I'd made an error in the voltage doubler, so I've redrawn it. The connection to provide a DC path for the high voltage supply back to the filament is the vertical line between C2 and C3. The "ground" symbols are just notional, and avoid having too many crossing lines. The circuit doesn't care. If I were measuring things, I'd actually use the aforementioned vertical line as my "zero volt" point (which is why I had originally tacked on a ground symbol there). The anode/grid supply is from the bottom of C2 to the top of C1, and the filament supply is from the right side of C3 to the right side of C4. The common point to both of these is the bottom of C2, which is connected to the right side of C3, which is why I chose it as my reference point, from which I can measure both the filament voltage (to the right side of C4) and the anode/grid voltage (to the top of C1). Clear as mud? All that said, I still prefer my later design, which saves a capacitor, and has a series-capacitor style voltage doubler:
<<inline: vfdps1.gif>>
<<inline: vfdps2.gif>>
In this drawing, "ground" is still there simply to mark my "zero volt" reference that is common to both supplies. The filament voltage is from "ground" to the right side of C3. The grid/anode voltage is from "ground" to the top of C2. I decided to inline both diagrams, to avoid having to look back and forth, and because I've been having issues with my web server. - John
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