Simple Audio Oscillator design and implementation :
An audio oscillator produces repetitive frequencies in the audio range, about 16 Hertz to 20 kilo Hertz. Audio Oscillators work by converting direct current from a power supply to an alternating current signal.

scheme

experiment :

https://www.youtube.com/watch?v=OZbFRPxTP18

 

Are you sure you have that cap polarity right?

 

A 4 Ohm speaker load may well draw ~1A and will probably blow T2, which is rated for 200mA.

 

That thing is not an "oscillator", it is a buzzer.