> > 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? -tony
