On Oct 13, 2015, at 1:22 PM, tony duell <a...@p850ug1.demon.co.uk> wrote:
The Versatec electrostatic plotters are not the same as the VT52
printer, they are
yet another process. WIth those the paper passes between a set of
electrodes that
build up a charge image on the paper. I beleive the paper is specially
treated to
make it more resistive so the charge doesn't leak away too quickly, and
there is
Yes, I had a bunch of Versatec 1200A's with the Tektronix
hard copy feature. the Versatec was the greatest graphics
printer until laser printers came out, then they became
instant boat anchors. Here's the process.
There is a double-sided PC board that touches the face of
the paper end-on, so the traces just come to the end of the
board and make contact with the paper. On the 1200A, that
was a 200 DPI printer, so each side of the PC board had 100
traces/inch, and they were interleaved, so you got to paint
200 raster lines/inch along the axis of the paper. The back
side of the paper had wide electrodes that defined zones.
One of these backplate electrodes was charged at a time to
the opposite polarity of the front electrodes. I seem to
remember there were +800, -200 and -800 V power supplies.
The raster line was written about one inch at a time across
the page, then the next backplate was charged and the next
inch was written, etc. Once the whole line was written
electrostatically on the paper, a stepper motor advanced the
paper and the next line was written. About an inch from the
writing electrodes, there was a toner applicator that
produced a fountain of this hydrocarbon-smelling solventy
stuff with the carbon toner suspended in it. The charge on
the paper would attract the toner particles, and when the
solvent dried (assisted by a blower) it pretty well stuck to
the paper. The paper had this awful chalky feel on the
print side, the toner smelled like printer's ink, and when
it was working really well, the paper came out gray with
fairly decent print.
But, it was FAST!!! It could print at about 1000 LPM in
print mode, and if your computer could feed it, it could
plot images (black and white only) at better than a page
every 10 seconds or so. So, it could actually run faster
than most of today's laser printers - although the print
quality, of course, was WAY worse. And, with the Tek
hardcopy board, it could hardcopy a Tek storage tube
terminal in less than 30 seconds.
I still have some Versatec printed output, as I ran one here
at my house for a couple years, from my MicroVAX.
We did have a TEK hard copy unit before the Versatecs. That
was a pretty awful unit. it had a line-scan CRT with a
fiber optic faceplate that exposed the image onto
thermal-developing silver paper-film that rolled past the
CRT. It also made bad smells, and the paper came out brown
with dark brown images on them. In normal fluorescent
lighting, the hard copies started turning totally brown
after just a day or two. Also, the silver paper was QUITE
expensive, maybe close to a Dollar a page or something, even
back in the 1970's.
Jon
