I've been playing around with fundamental circuits (no professional EE background), and became interested in oscillators. I have been trying to build the Hartley oscillator as described here. The document states that "an Hartley Oscillator circuit can be made from [...] a pair of series connected coils [...]".
I had a couple of 22mH fixed inductors, which I hooked up on a breadboard with the other needed pieces. When I test the transistor amplifier independently, it seems to be working. However, there is no sign of oscillation in this circuit.
So my ignorant question is, can I use the fixed inductors indicated? I saw mention of the notion of 'mutual inductance', and I'm not sure you can get such with these discrete components.
My friends and I started out by copying Oli's quick circuit, and were gratified to get a crisp sinusoid waveform. Thanks, Oli!
However, I clearly still have a long way to go, as when we attempted to change the frequency of the circuit we were mimicking, we got zero oscillation. And the original Hartley circuit remains stubborn.