Signal path: aerial → tank circuit (coil L ∥ variable capacitor C picks one frequency, f = 1/2π√LC) → grid of the triode. The tiny grid voltage gates the cloud of electrons boiling off the hot cathode. The plate circuit, fed 90 V by the B battery, copies that gating as a much larger swing — that is amplification. The output transformer drives the speaker.

Electron flow (real electron direction, not conventional current):

Drag to orbit · pinch / ⌘-scroll to zoom · turn the tuning knob to find the three stations.