On Sun, 2 Oct 2005, David Van Horn wrote:

> Although these voltages are relatively low, the flyback transformer
> method might work. The filament voltage for the rectifier tube was
> commonly done by a one or two turn winding around the core, heavily
> insulated, because the filament was way above ground. In this case, you
> may just take the filament current from your battery supply directly.

In a transistorised scope the cathode and filament would be at - a few 
hundred volts wrt. the main transistor chassis ground (the one that 
powers the X and Y amplifiers).

A flyback or push-pull converter is not so hard to make.

Peter
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