Heathkit HD-1416 Code Practice Oscillator

Heathkit HD-1416 Code Practice Oscillator

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.

 HD-1416 and key
The circuit consists of two transistors in a multi-vibrator circuit and one additional transistor as audio amplifier for speaker-level output(schematic below). The tone control is only accessible inside the plastic case. In the catalog ads notice that later versions are labeled with an "A" or "H" suffix and are slightly more squared with two black binding posts and a case color change to brown (A) and later black (H).

1979 catalog ad left and 1990 ad right. Note price change.
 HD-1416 ad 1979 HD-1416 ad 1990

1988 catalog ad
 HD-1416 ad 1988

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.

The HD-1416 used with the Heathkit Novice training course
 HD-1416 and Novice course ad 1979

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.

HD-1416 Schematic
 HD-1416 schematic

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.

date: 1-24-15

A Pyramid PS-21KX high power low voltage power supply was the previous item "on the bench".

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