PLAN B analog blog

I received 2 Model 15 VCO's a few days ago and I'm completely blown away by them. 
Everytime I plug in I seem to get something new in terms of modulating them in various 
ways. I was just listening to the first part of "A Sky of Cloudless Sulfur" by Morton Sunotnick 
and I was wondering how he got those tones in the very first part. I understand the track was 
made using a Buchla and the Model 15 core is very similar to that of what Morton probably 
used. Anybody have any idea of how Mort abused those oscillators to make them sound like 
that?! What waves do you think he started with? Intereting.
Thanks,
John