I use 2 BJTs, the NPN 2N3904 and the PNP 2N3906 wired in a push pull configuration to demonstrate AC through a modified polarity indicator circuit. I am using a DC power source, but this circuit works, with some modifications, on low voltage AC, or split power supply as well. I designed this circuit to help people who are wondering how the BJT push pull configuration. https://www.youtube.com/electronzap https://www.patreon.com/electronzap https://www.twitch.tv/electronzap https://twitter.com/electronzap https://www.facebook.com/electronzap/ https://www.reddit.com/user/electronzapdotcom https://www.reddit.com/r/ElectronicsStudy/ https://www.pinterest.com/electronzap/