I think you are looking at a manual for a later model bridge. My 650A
manual has the formulas but not charts.

Yes. However, in the 650A manual there is a similar statement. At page 3, item
9, they say that the bridge measures the series capacitance, and they also give
the formula for calculating the parallel capacitance (that is what we need, as
the leaky capacitors have a resistence in parallel).

I remeasured a bad cap and calculated the parallel capacitance, series
resistance, and parallel resistance. This is a paper cap rated at 0.02 uf. The
values I got a
Cs = 4.8 uf
D = 0.3
Cp = 4.3 uf
Rs = 994 ohms
Rp = 12 kohms

Not a very good cap.

Your Cp/Cs ratio corresponds to that calculated using the formula at page 3.
However the other figures do not tie up with what my spreadsheet gives at 1kHz,
that is:

- for measured Cs= 4.8uF and D=0.3 (that is a reactance / resistance ratio =
3.33), then Rs should be about 10 ohm, rather than 994 ohm

Moreover:
- the series of 4.8uF and 994 ohm would corresponds to Cp= 5,335 pF and Rp= 995
ohm
- the parallel of 4.3uF of 12 kohm would corresponds to Cs= 4.3uF and Rs= 0.1
ohm
I get values close enough to yours only if I set a frequency close to 10 Hz, not
1 kHz (unless I did something wrong).

Anyway, you may measure the parallel resistance of your capacitor with an
ohmeter, and check that you really read a value as low a 12 kohm.

New plastic film caps measure very close to the marked value and have a D
which is below the residual of the bridge (essentially zero)

While there is an error from the rather high D it is not significant in
terms of this measurement, that is, the value of the cap measures nearly three
times its marked value.

why just three times? I would say that the ratio between 4.3uF and 0.02uF is
more than 200

I have not dissected one of these but suspect the winding is
distorted. That would also affect the voltage rating. What I mean is that the
plates of the capacitor are closer together than originally, probably because
of loss of the wax impregnant. I found other caps in this RX which had high
values so this one is not unique.

I have not measured the caps at RF but I seems like an interesting project and
a practical use for my Boonton Q-Meter:-)

BTW, I think my math is OK but maybe not.

73

Tony I0JX - Rome, Italy