A Cause of Instability

Radio Record, Volume V, Issue 26, 8 January 1932, Page 15

A Cause of Instability

N often unsuspected cause ‘of instability in a receiver is the undue proximity of certain . connecting wires; for example, grid. and plate leads. This is quite likely to cause uncontrollable oscillation. Sometimes it is found that the wiring cannot be spaced further owing to the disposition of the components,~- and it may be thought undesirable to alter the layout. In. such a case, if some of the more important wires, such as the grid and plate leads mentioned above, are cased in earthed metal tubing the set can often be made ecompletelv stable.

This tubing should, of course, be of fairly large diameter, or otherwise its — presence will throw.a large unwanted © capacity across the tuned circuit and — render ganging, if this is used, difficult. In this case the internal diameter of the tubing should be at least twice the external diameter of the wire, including its insulating sleeving. Soft copper or brass tubing may be readily obtained for this purpose, or as an alternative metal braiding may be used. For a temporary substitute, ordinary tinfoil may be wrapped round the insulating sleeving of the leads which require screening, and held in place by binding with a length of thin bare copper wire, the free end of which could be connected to the nearest point of the earth potential.