I just missed this one on ebay. These are very interesting looking synths, and I have only ever seen one come up before about 10 years ago. This one was in NJ USA so would have been a complicated buy from here in the UK as the seller wanted to keep it in the US, but it went very cheap - £450. This video was made by the seller I believe, who is called fsiz. It came with an Apple IIe computer and the editing software. Damn!
FROM THE EBAY AUCTION:
"A very interesting and almost historical synthesizer.
Tone color / quality / character could be described as simply unique.
As far as I know, there are not many K150s made, and K150s are one of only a few (hardware) additive synths ever made.
And, it's a Kurzweil, meaning that there is something about the sound, beside and beyond all the specs and numbers. If you ever have owned a Kurzweil before, you know.
This military / heavy industrial looking K150 is in full working condition (all buttons, display, connections, etc.) except the headphone output.
There are cosmetic imperfections here and there.
It is completed with an Apple II system with a MIDI interface card and software. It will definitely save you hassle of searching, getting, waiting, etc, etc...
This Apple II functions as the dedicated graphical patch editor and librarian, using SMP (Sound Modeling Program) software from Kurzweil.
Without this Apple II system, as far as I know, it will be almost impossible to edit. (possible but 240 partials! editing from the front panel?)
The Apple II is completed with a dual / double floppy drive, and a CRT monochrome monitor (green letters!)
They are all in good working condition with cosmetic imperfections, including faded colored plastic parts.
Comes with power and other cables for Apple II, floppies which contains SMP, printed manuals and other documentation, including schematics."