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RE: Cheap DC Filament PS

I haven't decided yet on the best way to handle the startup surge. An oversize switcher defeats the purpose of keeping everything small. The switcher has to fit under the chassis, so its size is more critical than a filament transformer mounted topside.

I'm trying to focus more now on alternatives driven by the electrical/mechanical requirements, rather than starting with the solutions themselves. For example, let's say a raw supply (transformer-rectifier-filter) is used to provide DC filament power. That saves under-chassis space, but the output needs to be regulated down in order to create the right voltage. That's where the problem comes in. The regulator usually controls a fairly large voltage drop, often at several amps, so it gets hot and needs a heatsink. There goes the additional space freed up by locating the transformer topside. In my case, the issue is even more difficult, because I want the output to be switchable from 6.3V to 12.6V. That means the raw supply must be at least 15V, and the drop to 6.3V will create a lot of heat.

From a problem-solving perspective, the best solution might be to combine a raw supply using a topside transformer with a small buck converter under the chassis. The buck converter could be programmed to provide 6.3 and 12.6 VDC from the same raw supply, and because it's so efficient, no heatsink would be needed. The only thing is, I don't know whether the typical buck converter will start the tubes when they're cold. I'll test that on the bench soon.



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