Ameco produced several code practice oscillators, including an older version of this tube type CPO . The older version of the model was advertised in Popular Electronics in June 1957. This version of the Ameco CPS is the later much safer circuit. It uses an oval speaker in place of a round one and uses a separate escutcheon on a black wrinkle cabinet in place of the earlier silk-screened cabinet.
This simple circuit hummed more than oscillated. I assumed the electrolytic was bad. Instead, I found an intermittent solder connection. The ground side of one of the two electrolytics had never been properly soldered to a terminal point that had five wires connected to it. Four of those five wires were properly soldered but the fifth was loose. This is a common problem especially in kit-built devices. While I had the little chassis out, I also used contact cleaner on the tone and volume control potentiometers.
Reviewing the circuit
Although this Ameco CPS has an AC-DC circuit without a power transformer, its circuit is a great deal safer than the earlier version.
This Ameco has no exposed high voltage hazards. The only exposed points on the terminal strip are to the output transformer secondary. The volume control is simply a potentiometer across the output transformer secondary. The code key simply connects and disconnects the speaker. The circuit also does not unload the output transformer secondary with the key open. The secondary always has the full 20 ohm resistance of the potentiometer across it, avoiding the problem of high pulse voltages in the transformer primary. I consider this later Ameco circuit to be one of the best of the simple AC-DC code oscillators for safety.
N4MW specializes in collecting code practice oscillators. He shows several Ameco models including this one. His site has a pdf copy of the instructions and schematic for the older version of the Ameco CPS. Those instructions apply to this version as well. The Ameco instructions include information for conversion to CW monitor.