The circuit shown in the figure makes use of a programmable unijunction transistor of type BRY39 and generates sawtooth signals whose frequency depends on the value of the capacitor used and which can reach a few hundred kilohertz. The frequency adjustment of the generated signal is made in the trimpot that acts on the base of Q1, which in turn works as a constant current source to guarantee a linear capacitor load. The supply voltage can be between 9 and 12 volts.
