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Radio Record, Volume IV, Issue 20, 28 November 1930, Page 29

Loftin-Three (Continued from page 17.) tended to allow of the audio amplifier being placed at the left hand side with the tuning’ dial in the centre. The arrangement is made thus so that the amplifier will have to be turned round with the screen grid valve to the right. Those who have made up the original

amplifier must adjust the wiring of the input as is shown in the diagram in this issue. By making the connections, which by the way, are shown in the diagrams »f both the systems, there need be no trouble when changing over from gramophone to radio. The remarks made con-

cerning the arrangement of the gramoradio switch hold for this circuit. The shield must be regarded as the negative, and all connections shown earthed must be made to it, ‘Vhis is then connected with B- of the amplifier. "Amplifier input" is connected between the 500 ohm. resistance and the 50,000 ohm. biasing resistance at the end of the detector circuit. This is the point between R1 and R2,

If there is any difficulty to stabilise the system and efforts directed toward reducing the turns on the primaries are unsuccessful it will be necessary to incorporate an r.f. choke and condenser in the output. The choke is connected in series with one of the leads to the speaker and the .001 mfd. condenser connected between the set side of the choke and the ground. It need not be stressed that this condenser should be able to withstand the voltage coming from the amplifier which is in the order of 500 volts. It should thus have a test of 1000 volts. We have now fairly fully treated the three valve systems. Next week we shall go a step farther and consider the Loftin-White system applied to a fourvalve set, using the 250 type valve and the power pentode. Furthermore, we hope in the near future to publish the constants for the new E406 valve.