VT101 screen adjustment

tony duell ard at p850ug1.demon.co.uk
Tue May 10 10:04:21 CDT 2016

> > Another good practice is to use several carbon-composition resistors in seri$
> Actually, that makes me curious.  Would a piece of pencil "lead" be a
> workable substitute?  I could imagine taking a drafting/art pencil lead
> (the kind that's some 2-3 mm thick) with clip-leads, one on each end.
> (Preferably inside some kind of container, so the connection on the HV
> end is not exposed.)
> But I don't know whether its resistance would be too high (or too low,
> though that seems unlikely)....

Actually pencil lead is suprisingly low resistance. Try sharpening a pencil at
both ends and measuring it.

When I was younger, I carefully cut and split a pencil apart lengthways. This
left me with the lead in a trough of wood. A wire wrapped firmly round one 
end and a wire wrapped round that I could slide along made a reasonable
varialble resistor. I can remember using it with a battery (probably about 4.5V
to 6V) and a torch (flashlight) bulb as a dimmer, so the resistance can't be
that high. 

The resistance does depend on the grade of pencil. The more 'black' it
is. the lower the resistance. So a 6B has low restance, a 6H high,

Of course we are all talking about rods of graphite, not the metal lead, right?


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