I have uploaded photographs (albeit cr@ppy) of the output
waveforms of the Model 15 prototype.

Go here:

http://www.buzzclick-music.com/model_15.html

and scroll...

Please note: It was difficult for me to get these photos in focus
(as you'll see, I wasn't all that sucessful) in the process, I did not
check the zero crossing alignment of the waveforms on the
scope. They're symmtrical to zero!

- P