CABLES 



motion drives with ratios of 100 : 1 can be obtained. In checking over a 

 particular drive before use it is essential to ensure that it is free from backlash. 



CONNECTING WIRE 



By this is meant material used to wire-up the inside of apparatus. Tinned 

 copper wire insulated with PVC seems to be universal for wiring up electronic 

 equipment nowadays, except that polythene insulation is better for EHT 

 connections. Two procedures are clearly possible: to buy insulated wire 

 and remove the insulation as necessary, or to buy bare wire — say 22 gauge — 

 and slip on PVC 'sleeving' as required. For general work the writer prefers 

 the former method, but the latter is quicker when half a dozen or so tags, 

 rather close together, have to be connected. 



Insulated wire may comprise a single core conductor of about 20 gauge, 

 or may be 'flexible', i.e., stranded. Single conductor wire will take sharp 

 bends, and equipment connected up with it, when the work is performed by 

 an expert, looks extremely smart. In the hands of a novice the result is less 

 happy, as every accidental bend to which the material is subjected leaves an 

 ineradicable kink. The writer greatly prefers working with flexible wire 

 which, if it does not make smart bends, at least takes up a course of graceful 

 curves automatically. 



Flexible wires are described by two figures separated by an obhque stroke. 

 The first gives the number of strands, the second the diameter of strand in 

 inches. The common flexible wires are : 



Of these, the first two are much the most important. 7/0-0076 is 'Instrument 

 flex', only about 1 mm in diameter with insulation and, in virtue of its 

 pliability, excellent for making lightweight connections to electrodes on 

 animal preparations. It may also be used for general wiring work, but the 

 insulation melts rather readily during soldering. Much easier to use is 14/0-0076, 

 which, with insulation, is about 2 mm in diameter, and the writer strongly 

 recommends this for the bulk of electronic wiring; for valve heater leads it is 

 advisable to use a heavier gauge. 



CABLES 



Cables consist of one or more insulated flexible wires, with or without 

 'screening', i.e., a braided metal sheath which is earthed. Cables commonly 

 have between one and seven cores, though types having two dozen or more 

 are obtainable. The cores themselves are commonly 14/0-0076. The insula- 

 tion may be PVC or polythene. If the cable is screened the screening may be 



22 325 



