Radio Broadcast (May-Oct 1925)

RADIO BROADCAST ADVERTISER 11 General Theory of the Toro -Trail Figure i shows how the field of the ordinary coil extends into space and increases losses due to stray field. Figure 2 shows a "double series" winding, which restricts the field somewhat. Figure 3 shows a "four series" winding and the field almost enclosed. In Figure 4 (the Toro-Tran) the field is entirely enclosed and the losses due to stray fields are eliminated. Note that a stray signal passing through the coil at "X" — not introduced from the aerial or the tube — is balanced out at "Y" by the reversed polarity of the winding. This rejects undesirable signals, while the concentrated internal field builds up the tuned signal. Hence maximum distance and selectivity. and now the TORO -TRAN ! CARD WELL, whose pioneer "low -loss" condenser established new standards of radio efficiency, is now introducing the Toro-Tran* — the ideal balanced coupling inductance for all radio frequency work. *TRADE MARK Registry applied for The Toro-Tran eliminates signal energy picked up by ordinary coils from nearby stations. It eliminates magnetic feed-back in multi-stage radio frequency circuits, thus removing the most active factor in causing howling and distortion, and thereby increasing selectivity and distance. It rej ect s almost entirely the interference effects caused by electrical power machinery, elevators, door-bells, arc stations, etc. The Toro-Tran winding confines the field to the inside of the coil, a small area, and thus avoids one of the greatest causes of loss known to radio receivers— that of stray magnetic fields, which result in the absorption of signal energy and reduce the efficiency of the receiver tremendously. Note these unusual advantages in assembly and operation 1. Compactness. The coils do not require spacing or angular mounting. They occupy less space than your condensers. 2. Permit exact nullification for tube and stray capacity without guesswork or tedious testing. 3. Closed magnetic field eliminates magnetic feed-back in tuned radio frequency amplifiers. 4. Low distributed capacity, due to air spacing of each winding and to low voltage-drop per turn of small diameter wire. 5. Maximum coupling and high ratio of voltage increase due to concentrated field with zero leakage. 6. Absence of all supporting insulation in the field of the coil. This is one of the greatest loss factors in the ordinary circuit and is not remedied by "skeleton" or so-called "low-loss" windings. 7. Ease of neutralizing oscillation due to tube capacity by means of rotating control, which anyone can "balance." 8. Low capacity between primary and secondary, affording maximum transfer of energy to succeeding grid circuit. The Toro-Tran has a lower "circuit resistance " (i.e., effective resistance as assembled in a set and not as isolated in the laboratory for theoretical measurements) than any inter-stage tuned transformer made and has a correspondingly higher amplification factor, its ratio exceeding ten. To appreciate the many remarkable advantages of the Toro-Tran, write for our two free booklets: "The Torodyne Circuit" and "The Most Interesting Radio Frequency Transformer Ever Invented." Toro-Trans are ready to mount in any tuned radio frequency circuit. Replace your ordinary coils with Toro-Trans. You will be astonished with the results. Most .00035 mfd. variable condensers will tune them, but by using Cardwell Condensers you get maximum efficiency. Order from your dealer or direct CARDWELL TORO-TRAN WITH BALANCING POTENTIODON $ 4.00 Cardwell .00035 Condenser for tuning 4.75 Cardwell .00035 Vernier Condenser 6.25 Cardwell .00035 Dual Condenser (two-in-one) 8.00 Cardwell .00035 Triple Condenser (three-in-one). . . . 12.00 Cardwell Audio-Trans (compound audio transformers) 10.00 The Allen D. Cardwell Manufacturing Corp. ^ 81 Prospect Street, Brooklyn, N. Y. if Tested and approved by Radio Broadcast it