John Pearson 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?


Normally this is called a "decade box" and most labs
and good workshops have them.

Use 10-position rotary switches, one for each "decade"
of values. It can then be ANY capacitor you
need just with turning a knob.

For max ruggedness:
* use 2kV ceramics for the very small sizes <1nF
* use 630v polyester for the mid sizes <1uF
* use 160v NP electros for the larger caps.

A good decade box is really wonderful to have
when designing circuits. If you make a good one
it will save countless hours of calculating and
trial-and-error over the next 20 years...
If you are going to do this I suggest using all
values, not just >1uF. You will appreciate it
on your next project.

One caution, electro caps are typically 10% to 20%
higher capacitance than their marked value. If you
want to get the ranges accurate you may need a
capacitance meter and some fiddling with values.
:o)
-Roman

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