|Knightkit Star Roamer|
"What?", you say. "This is a receiver, not a code practice device." The thoughtful designers at Knightkit decided that a beginner's receiver would be used to learn to receive morse code. But what about sending practice? They cleverly and cheaply built in a "code/normal" switch and a terminal strip to connect a key (see inset picture below). In the "normal" position, received sound is emitted from the speaker or headphones. In the "code" position, the audio output is interrupted by the open key circuit. To practice code, put the switch in "normal", tune in a carrier and adjust for a constant beat note. Then switch to "code" and operate the key. No special oscillator involved, unless you count the distant station emitting the received carrier wave.
Documentation (the complete construction/operation manual) is available from the Boat Anchor Manual Archive.