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

Brent Hilpert hilpert at cs.ubc.ca
Tue Oct 13 13:43:58 CDT 2015

On 2015-Oct-13, at 8:25 AM, Paul Koning wrote:
>> On Oct 13, 2015, at 11:19 AM, Jay Jaeger <cube1 at charter.net> wrote:
>> On 10/13/2015 12:02 AM, tony duell wrote:
>>> ...
>>> It appears to be electrolytic. You have to keep the paper damp (there is a wick
>>> inside that you put water on. The paper goes between a helical electrode on
>>> a spinning drum and a straight strip, the latter being replaced when you fit a new
>>> roll of paper. Whether it is some chemical in the paper that changes colour, or metal
>>> depositied from the electrode I don't know (the former seems more likely). 
>>> I have never got it to work. Whether that is due to electronic problems (that I can
>>> fix) or chemical problems with the old paper (which I can't) I don't yet know.
>>> -tony
>> I had a little Comprint printer in the 1970s/1980s that used something
>> sort of like this.  The paper was aluminum coated, thus conductive.  The
>> head was a high voltage electrode unit that burned away the aluminum
>> layer.  (I can't imagine any kind of deposition technology in that
>> era...).  The head flew back and forth really fast, doing one pixel-line
>> at a time.
> There are all sorts of oddball printing technologies from back then.  I remember one (from a lab instrument, not a printer or terminal) that used aluminum-coated paper, but the coating was on the back of the paper.  The writing was done with a high voltage electrode just as you describe, but the result was that the sparks would scorch the paper and leave a thin black mark.

TMK these were generally referred to as electrographic printing.

This sort of scheme goes back to at least the 40/50s for fax machines:
There the metalisation is on the back of the paper.

Similar technique used in an early 70s calculator, but the metalisation is on the front:
John Wolff describes the mechanism in more detail:

( In these designs there's no wetting involved.)

> I don't remember what the VT55 used.  Tony's comment does sound plausible; I distinctly remember "electrolytic" printing technology though no details.  I wonder if it might help to take a bit of the paper to a competent chemist for analysis, to find out what the active ingredient is.  That might help give a clue what is needed to make it work.
> 	paul

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