Simple code-set oscillator for operation on AC or DC. It has practically universal application.

FOR those of you who are keenly interested in learning telegraph code, here is a practice set which can be made at home. The unit is a simple oscillator, not a buzzer set, which uses neither audio transformers, batteries, nor tubes. It will operate on AC or DC at 25 to 60 cycles, 85 to 150 volts. If the volume of the tone signal is too loud on AC, a 100,000 to 250,000 potentiometer can be connected across the two .05-mfd. paper tubular condensers to allow a varying control of volume. Besides these tubular condensers the only other parts required are a rotary or toggle on-off switch, two Fahne-stock clips for the phones, and a microphone plug and jack for the key. Any type headphone or earphone will do. A simple homemade key, for those who wish to avoid the expense of buying a regular professional instrument, is shown in one sketch. Don't steal the knob from a cooking utensil; a new one costs only a few cents.

View of the oscillator from the underside. The paper tubular condensers may be connected with a potentiometer if tone-signal volume is too loud.

Complete wiring diagram showing all connections for the code oscillator, and, left, a sketch to aid in the construction of a simple sending key.