Have you considered a 'power' integrator? Basically a power amp (or op
amp) driven as (or by) a traditional integrator. Change your series R,
and you change your equivalent capacitor value. You get better than a
real capacitor characteristics (although you could add leakage and
memory terms with suitable circuit elements).
 A variation on the op amp gyrator (pseudo inductor) idea.

Spehro Pefhany wrote:
>
> At 05:40 AM 2/22/01 -0800, you wrote:
> >I want to build a 'dial-a-cap' for experimenting with cap values in rather
> >slow rc networks.
> >
> >I will want values from 1 to 1000 uF and about 30-40 volts dc.
> >
> >What type of cap is the most versitile, rugged and usefull for something
> >like this?
>
> Nothing. Film capacitors would be too large. Bipolar and non-polar caps
> are leaky and so on. You could try back to back low leakage e-caps, but ..
>
> Best regards,
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Spehro Pefhany --"it's the network..."            "The Journey is the reward"
> speff@interlog.com             Info for manufacturers: http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:  http://www.speff.com
> Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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>
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