A Simple, Valve Curve Plotter

[ppppenguin]

Not sure if this one's been mentioned before. Get a small toroidal transformer, the sort with a hole in the middle. Then wind your own secondaries through the hole. A bit of experiment needed but it won't be more than a few turns for each volt of output. Bring out windings to clearly marked sockets and voila, Robert is your aunt's husband If you're rectifying and smoothing the output this will need fewer tuns per volt than if you're using the AC direct.

If I wanted a set of fixed voltages rather than fully variable I'd likely go for this approach.

I can probably let you have a toroidal transformer for the cost of postage.