On 4/12/24 20:21, Paul Koning via cctalk wrote:
On Apr 12, 2024, at 7:48 PM, Van Snyder via cctalk <cctalk@classiccmp.org>
wrote:
... The other was to print on its "whippet"
printer, a very fast electrostatic printer that put soot onto a thermal
paper that was then heated to "fix" it. There was a huge variac under
the printer to adjust the heater. The perfect setting was between two
windings. Too cold and the soot fell off. Too hot and it was melted and
smeared into an almost illegible mess. But it was very fast -- and only
80 columns wide. It was about the size of a KSR-33.
Different beast, but it reminds me of an electrostatic plotter we at on the U
of Illinois PLATO system. That one was by Versatec, either 11 or 17 inches
wide (I forgot), 300 dpi, pretty sure it used wet toner. It also used a chain
drive for the paper feed, which had enough backlash that starting and stopping
would produce visible irregularities in the output. So I wrote a driver for it
that did overlapped I/O to avoid that problem. (File I/O directly from a PPU
program, lots of fun!)
With that, it did an awesome job printing musical scores.
Yes, there were a number of Versatec models for different
paper sizes and pixel density. I worked with a bunch of
1200A units, they could run either roll or fanfold paper at
11" width. The paper was clay coated and felt like a dirty
chalkboard. The toner was quite smelly, some kind of
paraffin oil with carbon particles suspended in it. There
was a blower to evaporate the toner solvent. The 1200A had
200 pixels/inch, so you got 2112 pixels across the page,
IIRC. it applied 800 V to the writing electrodes, and
something like 400 V to the segmented backplate that was on
the opposite side of the paper. It could print text at
about 1200 LPM, which was pretty fantastic for the time.
But, I am glad to not have to deal with these things anymore!
Jon
