THE OSCILLATOR COIL So, the red can, the oscillator traffo is actually oscillating? Yes. Bring a working AM radio near it and tune it around. You will will pick the oscillation. It will sqeal.You can tune either the 1st or 2nd radio or both. Do you want it to be a pure oscillator? Well, see the plus going to the C coming via the yellow IFT. The red and yellow traffos are in series, right? Well, remove the yellow traffo and connect the plus to the primary of the oscillator. It will continue to oscillate without the yellow traffo. . Next, you don't want the incoming station, right? Well remove the antenna. What is left is an oscillator and it is tunable with the tuner capacitor. You can make an AM transmitter! But not now. THE INTERMEDIATE FREQUENCY, 455 KHZ. Let us start with the yellow traffo. The C of the first tranny drives this traffo, right? In the schematic, you will see that there is a capacitor across the 3 pins. It is a tuned coil! So the coil peaks at 455 Khz and rejects frequencies below and after 455 khz. There is a measure on how well it is doing this. It is called the "Q" of the traffo. The second tranny does the same thing to the white traffo as a driver. See where the 2nd tranny gets its signal. From the yellow traffo! Another tranny to drive the black traffo. With 3 tuned traffos, only 455 Khz gets through. It has been AC all the while. Now, look at the black traffo as like the traffo in your power supply project. Its secondary has 2 pins, right? Let's make a DC power supply but with very little current. Ground one pin and run a diode on the 2nd pin. Now it is DC! Let's filter it, so add a 1K Res with caps before and after. Remember in your P.S. project, you had eliminated the hum, the AC hum. And heard nothing. But the house electricity is steady. In the AM radio, the AC signal is fluctuating in strength. That's because the announcer is talking!