The Varicap Diode
I have not used one before but my reading suggests that they work pretty well as a "single" in receiver projects (refer to "B") but for (high powered) oscillators a "twin serial" set up (refer to "C") is recommended:
In each case value of "R" is not critical but 1M ohm is common. Usually a capacitor at "Vc" is added to minimise unwanted RF in the control voltage (Vc) circuity as shown in the following:
The 1SV149 (=1/2 BB212) Varicap
I purchased a couple of these some time ago off ebay. There is the datasheet (http://www.qsl.net/df7tv/datasheets/1SV149.pdf). At 1 volt the capacitance is about 485 pf and at 8 volts the capacitance is about 25 pf.
Using a 320uH inductor and a 1000 pf series capacitor the tuning range should be about 500 kHz to 1.8 MHz.