VT52s, VT61s lots of DEC and DG keyboards- return trip through Maine, MA, NY, PA, OH, IN to IL

tony duell ard at p850ug1.demon.co.uk
Wed Oct 14 08:55:17 CDT 2015

> 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.

Only in the sense that a PDP11, or a VAX, or a PERQ, or 
a <insert your favourite classic computer> is a boatanchor.

My view is that a computer is a lot more than the processor,
and that the peripherals should be preserved too. Yes the 
processor runs the old software, but emulators do that too, If
you are interested (as I am) in the hardware then the peripherals
are as interesting as the processor in a lot of cases

> 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

That's it. IIRC that was the 'Nib electrode' in Versatec manuals.
Somewhere I have a spare one for the V80 series.

> 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.

It's been a long time since I looked at the manuals, but IIRC 
the width of the back electrodes was half what you might 
expect -- half the 'repeat distance' of the nibs. The reason was
to prevent edge effects between nibs and the adjacent back

> 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

Was it a stepper motor? I am sure mine uses a permanent magnet
DC motor. I do remember that the paper feed roller is in 2 parts 
with a differential gear between them.

> 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

It's called the 'toner fountain' in the manuals, but it actually works
below atmospheric pressure. The results are that (a) the paper is
sucked down onto the toner fountain and (b) if the paper is torn
or runs out you don't get toner sprayed all over the machine room.

The toner is circulated by a little electromangnetic pump. The toner
system tends to block, I found that what we call 'white spirit' was a 
suitable solvent to unblock it. One time I tried the old 'suck it and 
see' method to get the pump valves working and found that the toner
tastes horrible!


> 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.

I don't have a Tektronix hard copy unit (one of the few oddball 
printers I've not managed to obtain) but I am told that the paper
goes off with time, and that it unlikely there's any useable paper
left for them ;-(


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