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.
We find this circuit in an English 80's documentation. The circuit can be made with more modern...
This old oscillator using germanium transistors has a high impedance headphone as inductor to...
This is one of many Morse code audio oscillators that can be found in this section. The circuit...