Here is a simple circuit for a one transistor Audion type radio powered by a 1.5 V battery. It employs a set of standard low-impedance headphones with the headphone socket wired so that the two sides ...

Sometimes, it is useful to transmit a low-power radio signal to create a beacon, to send a signal carrier to a near receiver, to transmit in QRP or QRPP mode, and so on. The circuit shown here is very ...

A very simple but highly efficient combination lock circuit is shown in the figure. Any type of on/off switches can be used, varying from commercially available inexpensive types to more sophisticated ...

With its "genuine superheterodyne circuit" and "standard 22½-volt battery," the Regency TR-1 not only launched portable audio, it also brought us gobbledygook technospeak. The Regency was the first ...