Beginners' Corner

Radio Record, Volume II, Issue 49, 21 June 1929, Page 13

Beginners' Corner

All-Wave Sets. LL-WAVE sets are usually in great demand, for the average constructor usually considers that in one set he can combine the virtfles of both broadcast and short-wave receivers, Not so; a sacrifice has to be made either to the longwave or to the short-wave receiver. Regarding this, "Radio News," the world’s largest and most popular journal, recently stated: "No large manufacturer has ever yet marketed a combined broadcast and short-wave receiver." ‘The reason is obvious, and to use the simile quoted from a recently-published catalogue, "the rea-

a son is that a Baby Austin and a Buick cannot both be built with the same engine. _ The peculiarities of the short-waves or frequencies demand that certain major alterations he made in the circuit to receive them, They are, briefly: 1, The coils have to be very much smaller. 2. The tuning condenser of very much smaller capacity than that used in the broadcast band, 8. High frequency amplification is rarely used except with the screen grid receiver. : 4, The set is rarely earthed. An all-wave set to be efficient on the short-wave must combine these features. In addition, provision must be made for tuning the broadcast band, and this usually by plugging in coils of greater length. But the tuning condenser cannot conveniently be altered, with the result that a coil of very great inductance requiring a very great number of turns must be used. This is not only inconvenient, but inefficient, and the all-wave set thus loses on the broadcast band. If a larger capacity condenser is used, it will be found that the tuning on the short waves will not be sufficiently sharp. For tuning both short-wave and broadeast band the best arrangement is an ordinary broadcast receiver with a shortwave adapter. which can be plugged into the amplifier of the broadcast receiver. Such a combination has been described in the latest issue of the "New Zealand Radio Listeners’ Guide." Some constructors have had quite good results, though it is emphasised that the best results cannot be obtained from an all-wave receiver. However, to meet a

-- -~ certain demand, "Pentode" will describe an all-wave receiver in a future issue. The Gramophone Pick-up. A CORRESPONDENT has asked ff he can connect a gramophone pick-up-to a Browning Drake. Certainly he ean. It can be connected to the audio stages of almost any receiver. There are mainly two methods of connection: (a) Using the amplification of the detector valve; (b) plugging into the detector but losing its amplification. To make an arrangement of the "A" type take a wire from the G terminal of the detector valve to one side of a jack. Connect the other side to "A" fasten @ plug on to each of the pick-up wires, and, when the gramophone pick-up is required; just plug in. . The other method requires a broken valve base. Clean away the glass, and unsolder the wires passing down the legs of this. Decide which of the prongs goes to the plate and which to the filament negative, and pass one lead from the gramophone pick-up to each. All that is necessary when the gramophone pickup is required is to remove the detector valve, replacing it with the base with the two wires attached.