Importance of By-passing

Radio Record, Volume II, Issue 25, 4 January 1929, Page 28

Importance of By-passing

‘A LTHOUGH the better grade manufactured receivers to-day are including by-pass condensers with a view to obtaining greater efficiency, the value of this practice is not always fully appreciated by the set-builder and experimenter. Both high-frequen-cy and audio-frequency currents should be provided with the shortest possible path, in all cases avoiding circuitous and high-resistance detours through batteries, mains supply units, transformers, and go on. Moreover, the audio frequency should be kept out of the H.F. end, and the high frequency should be kept out of the L.F, end, L.F. By-pass. TTAKING the detector and the first L.F. stage as a typical case, bypass condensers may be used to keep the radio-frequency component out of the transformer primary, and fo keep the audio-frequeney component out of the high-resistance B supply unit or B battery. , A suitable H.F. choke is inserted between the plate of the detector valve and the transformer primary together with a small by-pass condenser on the plate side of the H.F, choke connecting with the filament negative.

The audio-frequency energy is bypassed by a one-microfarad condenser between the B positive and the filament negative. This will be found to improve the tone quality and also generally the volume. The by-pass for the H.F. end invariably provides greater sensitivity and volume, particularly with a regenerative detector which may sometimes fail to oscil-, late freely in the absence of such bypassing. Volume and Sensitivity. Y-PASSING for the L.F. com pogéiet is provided by a filter Cond cggyyr of 1 or 2 microfarads between the B positive and the filament negative leads. ‘The use of a by-pass in this position results in better tone quulity and a reduction of background noises, whether with B supply unit or partly run-down B batteries. Generally, an amplifier not so equipped may be materially improved by by-passing all B positive connections to the filament negative. Finally, an H.F. by-puss -arrangement Which is not often employed but which will increase sensitivity and volume to a considerable extent in many cases is to place a by-pass cole denser of .00Gmfd. between the fila ment negative and the B positive lead which goes to the primary of the H.F, transformer. This will be found specially useful in causes where the B battery or the B supply unit has fonsiderable internal resistance.