Info about the 1967 original from the manual:
The new Astro-Tone distortion generator is the finest, most flexible, most durable unit of its kind available. One look at the heavy-duty cast housing will tell you that this unit is built to last. The hardest professional use will not affect the Astro-Tone.. The semi-conductors used in the Astro-Tone are all silicon. Many distortion generators still use germanium transistors, not the Astro-Tone. Forget about temperature changes altering the sound quality. Forget about maintenance. Most of all, forget about buying a replacement; you won't need one. This unit will last and sound better than any distortion generator you have heard before.
The Astro-Tone is turned on automatically when a cable from the guitar is plugged into the input. It will stay on until the input is unplugged. This makes it pretty hard to leave on accidentally when you put it away. The output cable simply plugs into the normal input of any guitar amplifier. -There are never any compatibility problems with the Astro-Tone.
The distortion is switched on and off by pressing the button on the face of the Astro-Tone. This alternate-action switch is designed for the hard use of foot-switch service. When the distortion is switched off, none of the three controls have any effect. When it is switched on, each control has a very different effect which makes possible an unusually wide variety of tone colors.
The volume control adjusts only the loudness of the distorted signal and is usually turned up high enough to provide a dramatic increase in volume when the distortion is switched on.
The tone control adjusts the form of the distortion and can alter the tone color of the output signal to mimic the sound of almost any unit on the market. Almost all of the available distortion generators can alter the amount but not the type of distortion which is generated. The great advantage of the Astro-Tone is the control provided over the form of the distortion which can be adjusted from rich to bright. The Astro-Tone provides a wide range of expressive tone colors which can be adjusted to fit the mood of the music itself.
The attack control adjusts the amount of distortion, but not the type of distortion. It is usually left almost at maximum to provide a clearly distorted signal, but may be turned down to soften the sound. If the attack control is turned to zero, no signal reaches the distorter and the distorted output vanishes. To insure enough drive to the distorter, the output of the guitar should always be set near maximum.