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

[Paul Koning]

> 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.

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