
Title link takes you to more shots via
this auction. Be sure to check them out. There are some great shots including a drawing of one, and a University of Illinois face plate.
Details:

"This machine was manufactured in 1972. The HSL-II has 3 sine wave generators, a square and saw wave fuzz generator (awesome!), and a pink and white noise generator. These can be seen clearly on the far left of the HSL-II. The signal path flows from left to right and is patchable with mini-banana cables (included in the auction). There are 3 filters which allow patching through hi/lo/mid pass sections. There is a phase inverter, limiter, frequency counter (with a classic red LED display) , 4 attenuators (volume), 2 mixer sections, a VU meter, and a few mystery functions that affect the sound but that I am not qualified to describe. there is also a gate sequencer, so you can basically set two different lengths of tones to trigger as you desire. The sequencer is weird and rudimentary, but functions perfectly.
Below are some long recordings of the HSL-II into a Deltalab Effectron Jr. digital delay. I ran this into a decent DJ mixer and into apple's Garageband. I clipped up the audio to make it a little shorter and give you an idea of a portion of the range that you can achieve with the HSL-II.
HSL-II sample one
Sound plays at beginning and towards the end - dead air in the middle
HSL-II sample two - plays fine

You cannot control the pitch from an external controller as of now. They were not designed for that. You can control the frequency manually, which in turn affects the perceived pitch, and believe me, with all 4 or 5 sound sources going through some delay and reverb, you have a wicked modular synth, sample source, drone machine....Silver Apples meets Aphex meets Eno.
I spoke with a synthe technologiste who thought that there would likely be a way to add c/v control to the sound source circuits...I have included a close up of a single sine sound source...it is the one circuit photo that has had the color altered and sharpened to give someone some idea what they are dealing with if they are so inclined to pursue the c/v route. Alas, there are no schematics and I have searched high and low on the internets.
The cabinet is absolutely VCS3-esque. There are a few areas of flaky veneer about the edges, as can be seen in the photos.
Also...you can run audio through the filters and even do some sort of weird sonic destruction by patching the fuzz output into the same input as the audio source. There are many many routing capabilities. These machines have provided me with plenty of inspiration. I will be moving soon, so please look out for all sorts of audio related stuff."
MP3s backed up
here.
The one via Must! who is the seller.