Heathkit produced the HD-1416 code practice oscillator from late 1974 to 1991. The price of $9.95 included an inexpensive Japanese-made key. Over the years, the price increased in several stages to $24.95 in the 1990 catalogs. Heathkit also sold the kit in conjunction with its Novice license course.
This simple circuit needed little more than a fresh battery and a cleaning including some DeOxit contact cleaner for the tone and volume controls, the phone jack, and the battery snap fastener.
Reviewing the circuit Early transistor code oscillators typically fall into two camps, the earliest being a single transistor circuit using a tapped transformer for the feedback path. The first Heathkit transistorized model CO-1 used that circuit. My first code oscillator kit, an Allied Radio Knight-kit, also used the tapped audio transformer and the famous CK-722 germanium transistor. I remember rigging the oscillator as a audio source for testing amplifiers. This version with a multi-vibrator circuit was typical of later circuits when transistors were considerably cheaper than transfomers.
Heathkit also includes instruction for using the HD-1416 as a side-tone monitor for transmitters using a grid-block keying (grounding a negative bias voltage with the key). A diode protects the oscillator circuitry from the transmitter's negative keying voltage.
N4MW specializes in collecting code practice oscillators.
He has made the manual available at this link although the quality of the copy is just fair.
A Pyramid PS-21KX high power low voltage power supply was the previous item "on the bench".