Instructograph

The video at right shows a the Instructograph code training machine I received recently (2024). I do not see a model number on it, but it has these unqique characteristics:

Tape takeup reel driven by a shaded pole induction motor with a conical capstan driving a rubber idler wheel. The motor position is adjusted to vary the speed by having the wheel make contact at varying diameters on the conical capstan.
An internal vacuum tube Armstong oscillator to generate the Morse tone. The schematic of the oscillator is here. Note that one side of the AC line is switched directly to the floating ground in the circuit as is common in many AC/DC circuits.

The only problem with the unit was a dried dual electronytic capacitor (2 x 20 uF, 150 V). This was replaced with a pair of 22 uF 160 volt electronlyics. The tone was pretty high frequency (maybe 5 kHz), but was brought down to something reasonable by adjusting the mica variable compression capacitor to maximum capacity.

Since the audio output is not isolated from the power line, driving a line powered amplifier that is not transformer isolated introduces a ground loop and significant hum. A solution is to use a battery powered amplified speaker like this one from Walmart. A video of it in operation is shown at the right.

Instructograph in operation.

Instructograph disassembled and test capacitor clipleaded in.

Closeup of oscillator board with new 22 uF capacitors.

Instructograph with Walmart amplified speaker.