Variable
Capacitor 200pF Total
This variable capacitor has two seperate variable capacitors
inside which are used connected in paralell to form one single
capacitor of higher value. The middle connection strip is
the common ground connection. The two sections have
maximum capacitances of 59.1 and 141.6pF and so form a total of
200pF. The two outer strips are connected together in the
terminal strip circuit. The schematic shows a 320pF
maximum type but the exact value is not important. The
smaller value will give a slightly reduced tuning range but this
also depends on other factors, like the stray capacitance of the
coil and circuits.
There are also two trimmer capacitors internal to this variable
capacitor which are used to add a fixed amount of capacitance
when used in other designs. They need to be adjusted for
minimum capacitance as shown in the pictures below.
Minimum capacitance is when the top semi-circular plate attached
to the screw is moved so that the lower static plate is
completely exposed.
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