The Moog 901 Oscillator is basically a 901A Oscillator Controller and a 901B Oscillator in a 3 MU panel.  There is an additional attenuated output for each of the four output waveforms

The 901 Oscillator is a 3 MU wide module.  This is probably the best example of an original Moog module as there have been no modifications.

The serial number label indicates a July 12, 1968 date code.  Moog did not give modules serial numbers until 1967 and started at serial 1001 so this is the 63rd 901 produced after assigning serial numbers.

Operation

The output levels were close to specifications and there is just a bit of offset in the triangle and pulse outputs.  I chose to not modify this original condition module.

The maximum frequency is 31.7 KHz.  Above that the module stops oscillating.  The triangle and sine waveforms are pretty distorted but the module would not be used at this extreme frequency.

At 5 KHz the waveform distortion is minimized for reasonably nice waveforms.  The notch at the top of the triangle is a bit pronounced.  Later 901B oscillators had improved filtering for this notch but I have no information if this modification was ever applied to the 901.

The minimum frequency (non-LO mode) is 1.7 Hz and the waveforms look pretty nice.

In LO mode the minimum frequency is 35 mHz, or one cycle every 28 seconds.

In LO mode the maximum frequency is 70 Hz.  The notch at the top of the triangle is a bit more pronounced than at the same frequency in non-LO mode.

The pulse width control will adjust the output from a minimum of 47.8% to a maximum of 91.5% duty cycle.

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