This circuit is from an 80's publication. It makes use of small 6 V x 50 mA incandescent lamps. The diodes can be general purpose or even 1N4002. The transformer is 6.3 V with 100 mA or more current.
This circuit is from an old American documentation using as indicators for the flip-flops neon...
This circuit that uses only discrete components (transistors) mimics the sound of an American...
July 1017 - Maxim MAX17290 and MAX17292 PWM boost controllers can now be purchased from Mouser...