This circuit is from the 1983 Intersil Databook. The circuit has an A / D converter for display of 4 and a half digits being powered by a voltage of 9 V.
This TTL circuit uses LED indicators and must be powered by a voltage of 5 V. The capacitor...
Low power RF transistors such as the BF494 or BF495 and even those in the BC series can oscillate well...
This switched power supply was found in a 70s documentation. The basic components are from that...