The power source shown for powering for small TTL circuits was found on a Radio Electronics Constructor from 1977. Of course this is an alternative for those who do not have a 7805 on hand or want a transistorized configuration to take advantage of a zener. We changed the circuit to be able to be assembled with modern components. The transformer must have 100 to 200 mA. For currents up to 100 mA, use a BC547 and for currents of 100-200 mA use a BD135.
