When I was a kid, I built this circuit. You hook up a small capacitor to the test leads or maybe a couple in parallel and the speaker will output a different pitch based on the test capacitance. I thought it was a fun learning tool and I wanted to show it to my daughter.
The problem is, it seems these kinds of transformers are rarely used any more. I'd like to find a way to modernize the circuit to eliminate it. The one I used was a 4K CT : 2K
I don't understand center tapped transformers well enough, or I guess the circuit in general to do this myself. Hoping to get some pointers.
I'd be fine with using a black-box amplifier IC, the idea is to play with caps, amps can come later.