CONDENSERS

Radio Record, Volume I, Issue 7, 2 September 1927, Page 14

CONDENSERS

There ate some parts of a wireless Gircuit in which condensers are essential, and others in which they are not essential though very desirable, Many beginners in radio observe their more advanced friends putting condensers into their sets here and there, without any apparent regard either for their position or their capacity value, and the fhewcomer is often at a loss to know jast where and when a condenser is going to be of use to him. | The more "optional" places for condetisers are across the windings of the ¥,.. transformers, across the high-ten-sion battery, and as a shunt on the *phones or loudspeaker. By-pass Condensers, As a general rule, any piece of appatratus in a wireless circuit which has a high resistance (or "impedance" to be more correct) should have a "by-pass" coudenser connected across it in order to provide an easy path for the highfrequency currents, Of course, the ease of passage of the high-frequency currents through fhe condenser depends upon the capacity of the latter, and in special cases (as, for instance, in the case of the tuning condenser) the value of the condenser has to be chosen or adjusted very carefully ; it is not, in other words, merely a ‘‘bypass"? condenser. The first place for a by-pass conGenser is across the primary winding of the first intervalve transformer. The current which is intended to flow through this winding 1s the rectified current from the detector, but there is @ small H.F. current as well. This will tot pass through the primary winding of the transformer if a suitable by-pass cofidenser is provided A -common walue for this condenser is 0.001 mfd.

Across the H.T. Battery. The next position for a by-pass is across the high-tension battery. The resistance of the H T. battery is a matter for conjecture; in a new battery it is comparatively small. perhaps 50 to 100 ohms, but in a battery which has been in use for some time, the resistance is apt to rise very considerably The effect of this resistance is much more serious in a multi-valve set and in certain special types of circuit, when the one H.T. battery is common to all. the valves. The internal resistance of the battery and its ill-effects can be overcome, however, by the simple expedient of placing a large capacity condenser across its ends.

By "large capacitv" in this contection is meant a condenser of anvthine from 0.1 mfd to 2.0 mfd.-the larger the better This condenser is sometimes referred to as a "blocking cotdenser’ It is certainly worth while to include it, even when the battery is new, and vou will often be surprised at. the improvement in reception Yor these large capacitv fixed condenSers it is often cotivenient to use "paver condensers," that is, condensers made up with sheets of tinfoil and inswating sheets of paner The hest tvne of large-capacity fixed condenser are the Manshridge condensers: Mensbridce condensers are made by the T.C.C amongst others, and are comparativelv clicap. In this connection it mav be well to mention that many amateurs eet the tinpression that anv old condenser will do for a blocking condenser, partienlariv across the H T battery It is, however, just as important to have a condenser which is perfect itn insulation here as

al coudenser Finally we come to the condenser shunted across the ‘phones or toudsneaker Art first sieht a telephone condenser misht seem to have a bv-nass action, and to be therefore unvdesiralle But as a matter of fact, it acts’as a. storave condenser, and in this wav materi. ally improves the recertion Sienals can, of course, he heard withont a telephone condenser, but it shonld he remembered that there is alweavs a certain amonut of canacitv in that part of the Cirenit even in the absence of au actua@ icondenser. Owing. to the fact that the ’nmhones and the HT hatterv often occur in) proximity in the circuit, some amateurs place a sinole laree canacitv condenser fieht across the two, hut this is not the best practice It is better, as alreadv indicated to place a large condenser across the battery, and a smaller one across the ’phones.