Reaction Condensers

Radio Record, Volume III, Issue 28, 24 January 1930, Page 30

Reaction Condensers

Se apeemmneenal A Safety Device ITH regard to reaction condensers, in some circuit arrangements ‘these may have a large voltage-the whole voltage of the B battery-across from one set of vanes to the other, and therefore, unless some safety device is included in circuit with the battery and condenser, it is clear that serious damage may be caused by an accidental contact between a moving vane and a fixed vane. A fuse is perhaps the simplest form of protection, and it has the advantage that, being of comparatively low resistance and free of inductance, it does not interfere with the other adjustments in the circuit. An alternative protection is a fixed condenser-which may be of the mica variety-introduced in series with the variable condenser. Of course this means that we are ‘again dependent upon the insulation of the fixed condenser, but generally the insulation of & good quality fixed mica condenser may -be relied upon with much more certainty than that of .a variable air condenser. The introduction of the fixed: condenser in series with . the variable condenser means that the setting of the variable condenser will be: altered, and if the fixed condenser is of too small a capacity, it may be that the desired resultant capacity is thrown outside the range of the variable condenser. A capacity of .002, even up to .005 microfarad, may be used for the fixed condenser, and it is important also that, in addition to an adequate capacity, this condenser should have mica insulation. If the condenser is not of appropriate capacity and quality, the overall amplification will be reduced and sharpness of tuning will be lost. -_