Radio today (Sept 1935-Dec 1936)

tubes. . . . This is so even if a 6A7 is used as the mixer. In the majority of last year's superheterodyne receivers, the 6A7 was used as a combination mixer and oscillator. In the modern receivers, the heterodyning signal from the oscillator tube is fed into the mixer tube via the screen grid of the mixer. The coupling between the oscillator and the mixer tube is a small fixed capacity. The grid, normally interpreted as the screen grid in the 6L7, is grid number 3. Signal beacon * The zero beat between the two frequencies. . . . That is the way the receiver is tuned. . . . Have you come across these Grunow receivers? . . . The signal beacon is a beat oscillator, fixed tuned, and resonated to zero beat with the intermediate frequency. If this oscillator is off calibration it will interfere with correct tuning, because it will zero beat with one of the frequencies, present in the sidebands of the carrier signal. Zero beat will then occur at some frequency other than the accurate carrier frequency. To align properly the signal beacon, tune the i-f. assembly accurately to the correct i-f. frequency. Then tune the signal beacon oscillator to zero beat with the test signal being fed through the i-f. oscillator. Make certain that you are at zero beat by slightly shifting the tuning of the signal beacon, above and below the zero beat point. Then reset to the zero beat point and check by slightly changing the frequency of the test signal generator. Any deviation of the test signal oscillator frequency from the correct i-f. signal should produce an audio beat signal in the speaker. For this final checking, you should not use modulation of the test signal. I-F. regeneration * The new Atwater Kent models 856 and 976 receivers employ a third winding in the i-f. transformer connected between the i-f. amplifier tube and the demodulator. This winding is connected between the plate and the screen grid of the i-f. tube and is coupled to the other windings in the associated transformer. A portion of the signal in the plate circuit is therefore fed back into the screen grid and a certain amount of regeneration, with consequent gain in amplification, is introduced. Schematic diagram is shown below. White transmission cable * Our living room has antique finished walls. This is not an unusual color, hence what we will say is not an extraordinary situation. In fact, we feel that the majority of living rooms, for that matter other rooms, have light colored walls. . . . An antenna installation was made and the lead-in was carried around the room. Transmission cable was used for the lead-in and it was necessary to cross the window moulding and some of the wall space to finally reach the floor. . . . The serviceman who made the installation unreeled the transmission lead-in. It was black. . . . 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