On 2006-05-25, Jim Lesurf wrote:
In article , John Phillips
wrote:

I noted, BTW, that the integrator used in the test setup employs another
capacitor which must be assumed to be linear for the test to work. ...

... my reaction was to feel the above didn't matter once we'd
established that the actual conditions of the test were of dubious
relevance. No point in worrying about details if the test situation was
orders of magnitude different to those which are of actual interest to us.

I agree that in the case of a coupling capacitor the ideal design drops
a negligible *signal* voltage across it. The article and its test are
of dubious relevance there.

However, consider the case of a single-pole RC filter. In the pass-band
substantially the full signal voltage appears across the capacitor.

So I suspect there can be relevance in measuring capacitor non-linearity
with significant AC signal level. I am not sure if in a valve amplifier
this may happen inter-stage with the sort of signal level the article
uses for the test, though. As an input RC filter the signal voltage
across the capacitor will be somewhat smaller than that used.

--
John Phillips