They're not that costly, Tony. The last one I bought (for someone else) cost about $5. Unfortunately they only unwrap wires that were wrapped clockwise, and many automatic wirewrapping machines wrap the opposing ends of a wire in opposite directions. Another limitation is that they were designed for #30 wire, and many backplanes, etc, were done with #26 or #28. #30 is the most common, though. Please see my embedded remarks re: cut-strip-n-wrap bits below. These were bought up by Advance Electric Co. which also makes the "Ad-Strip" Kynar wire without which they work poorly. Dick ----- Original Message ----- From: Tony Duell <ard(a)p850ug1.demon.co.ukTo: <classiccmp(a)classiccmp.orgSent: Saturday, July 22, 2000 3:34 PM Subject: Re: Un-wirewrapping (and re-wirewrapping) a PDP-16 for here! These bits are VERY expensive, about $250 US as opposed to $75 for the "normal" bit that requires you cut and strip the wires yourself. I've been using them since the late '70's, and have never found a reason to cuss them. I've found that this type of bit, when used with the appropriate wire (extruded one extra time after the insulation is applied, to break the insulation loose from the wire so it comes off automatically when prompted to do so) si worth its weight in gold. I have a couple of them and not only do they last MUCH longer than the standard bits, but they make the job go much faster. I wrap small circuits from memory rather than from a schematic, though as I age I find the circuits I can remember have shrunk have to pick out the wire length or cut it to size. It's not unusual to place four or five wires a minute when the wires follow a discernible pattern. Once the board's full and there are wires all over the place, it's a mite harder and slower going. They do sometimes break the wire instead of just the insulation requiring the wire be removed, including the broken-off end, but that seldom happens if the right wire is being used. The make *wonderful* connections and the tool lends itself very well to direct-line (strung fairly tight) wiring which allows for randomizing the noise/crosstalk better than bundling wires together. I've had a few cases where the wire breaks after handling, though the insulation doesn't. It makes visual detection of the "open" impossible. Fortunately I've only been embarassed a few times by this occurrence. > One hint that I'll give you. You'll probably want to bus some connections > together. Most people start and the first pin and wrap a wire to the > second. Then wrap from the second to the third, then the third to the > fourth, and so on. I locate all my busses and wire them first, since they go fastest and work most easily on a relatively empty board. Normally my circuits are designed in blocks and I wire and subsequently check one block at the time, except for the busses. It should be kept in mind that it is NEVER necessary to use more than two levels of wire. For that reason it's important to use the shortest available pins, provided that they extend far enough through the board to allow two levels to be wired. > This is a bad idea, because if you make a mistake (and you will!), you > may have to to take off _all_ the wires past the mistake. The unwrapped > end of the 'trapped' wire from (say) the 3rd to 4th pin (trapped because > you can't get it off the 4th pin without taking off the wire from the 4th > to the 5th, etc) may well not be long enough to restrip and connect to > the right pin. > Instead. wrap 1st to 2nd, 3rd to 4th, 5th to 6th, etc. Then go back and > do 2nd-3rd, 4th-5th, etc. If you make a mistake you only have to take off > 3 wires and replace them, not the entire bus. A little thought given to which pin-to-pin connections should be made on which levels makes the job easier. It's important that signals on the same busses be of about the same length and have about the same number of loads. I try to wrap all the level one (closest to the board) wires first, starting with the busses. That makes it easy to continuity-check them and know they're done. It is pretty important to check the level-1 wiring before going on to level-2, as it helps save wires-taken-off if you foul up a pin count or something. This is all particularly important where connectors are concerned. it's best if connectors are wired on level-1, since they frequently lie at one end of a bus or another. > -tony