This 1924 receiver uses a battery for the tube filaments and a high voltage battery for the amplifier and detector circuit. The speaker is kind of high impedance era.
This signal injector and tracer (follower) was found in an old American documentation. The...
The basis of this circuit is the HA2400 released at the time. The circuit is from a Radio...
Found in a 1980s English magazine, this trigger circuit can have different types of inputs...