My 18 year-old students have just learned that an LC circuit can be used as an oscillator or as an tuner, so I would like them to build either an FM transmitter or an AM receiver as a homework. However, the only trimmer capacitors I have right now are 3-40 pF. They could build their own coil with 22 gauge wire, which is fine for the FM oscillator, but not so much for the AM receiver since they would need something around 500 μH to be able to pick up an AM station (too many turns!). Should I buy bigger caps (hard to find variables with more than 100 pF)? Should I buy 500 μH fixed inductors?