The circuit shown is from old English documentation and can be made with BC548 transistors for low power ones. The 2N3055 must be mounted on a heat radiator.
We found this interesting circuit in a 1969 American documentation. It shows a solution with...
Here is a high-quality intercom for demanding readers. The circuit is from a 1982 documentation. Of course,...
This circuit can be found on this website in similar versions. The power supply is given in...