The Birmingham age-herald., 1922-07-09

f circuit of the detector should be
 variable whenever a soft" tube IS
 used at a detector. The soft tube, being a "gas content" tube, is eX- tremely critical in it's operation, and
 each tube has it's own characteristics. The result is-that it Is very neces- sary to have a variable HB' battery
 in order that the correct amount of
 voltage can be applied to the plate
 circuit to suit the particular tube
 that is being used. For hard" tubes.
 or tubes. that have amplifylng
 characteristics. a variable "B" battery
 Is not necessary; as these tubes are very steady in their operation and
 not at all critical to plate voltage. No Transmitting Sets
 c. In a c. ". transmitting set.
 would l be able to get as good re-
 suits with A. c. using self-rectlfi- cation as with A. c. rectified by an electro magnetic rectifier? For 10 or 20-watt c. W. transmitter. would fnductive coupling be better than conductive? How would no volts D. C. be used to supply the filament
 and plate voitages for detector,
 two-step radio and two-step audio- frequency amplifier with power operated loud speaker7 Would
 such a change bring in music loud enough for dancing g?-F. V. L. A. Self rectification will be much
 better than an electrolytic rectifier.
 Use the regular two-element vacuum tube for this purpose. Conductive
 coupling in oscillating circuits will
 be much better than inductive cop ling. The 110 volt D. c. circuit can
 be used to supply both filament and plate voltages for your receiving set, hut aff of the cufnmutator ripple of the D.
 c. generator, which will be amplified l by your io-frequency amplifiers.
 At the present time, there is no real 1 satisfying substitute for the storage
 battery. With the set that you de- scribe, it should be quite possible to I obtain music loud enough to dance by.
 Power Line Interference
 c. We have eecently installed a radio which Is located about twen-
 ty feet from the II 1000 volts of the
 railroad power lines. We are using
 the four-wire 'L" antenna, each wire
 being about forty five feet long. We have also tried an inside aerial
 Of about 100 feet. but we are unable
 to eliminate the machine gun effect
 coming from the railroad wires.
 Please let me know if there is any way that we can eliminate this rail- road interference?-R. W.
 1 A. The best way to achieve this ject is to place your aerial at right angles to the power lines. If this
 means that you are compelled to place
 the aerial so that it becomes anti directional as regards the broadcast | ing station, then I would suggest that you make it a "T" aerial in- 5 of A cfr crla xui
 aerial. 125 feet long. will be far bet
 ter for your purpose than your
 present four wire aerial.
 Leakage in "B. Batteries o. 1. Is there any drain on the
 "B" battery when the filaments of the tubes are not lighted? In other
 words, is 1t necessary to break the high voltage circuit by a series switch when the set is not in use? ?. What Is meant by the Statement 1 that honeycomb coils are not as good" as vario-coupled var}o- 1 meter set for 3s0-meter work 2<Does
 this refer to signal audibility, dis tance covered or sharpness of tun- ing? A. K.
 A. 1. There should not be any 1 current flow in the "B" battery when
 the fllaments of the tubes are not lighted, but you will find that the | inclusion of switch in the ''B' battery circuit will be of great as- sistance in a lot of ways and will
 cut down any possible ffakage that might otherwise occur. 2. The statement that honeycomb coils are not as good as the vario-coupler l meter circuit for short wave work refers particularly to sharpness of tuning and general handling of the set. This Is due to the fact that the l inductances in the honeycomb coll set are not at all adjustable, and | in order to vary the oscillating cir cults 1t Is necessary to do so py means of variable condensers, and when we get down to short waves it means that there is minimum amount of capacity needed to got down into resonance with tho snort wave and consequently the capacity coupling is at it's lowest value. For this reason they are not as efficient as the yario-coupler variometer set on short waves.
 Hard Tubes Must Me Used O. 1. Can use a IIv-200 and a I-V-2o1 vacuum tube in the Arm strong -generative set? 2. Is a grid condenser used? A. H.
 A. You cannot under any circum- stances use the UV-200. because It Is a soft" tube. and the system will not operate with soft" tube. You can. however. use a UV-20i. provided that you reduce the plate voltage somewhat and do not em- ploy more than 60 volts on any of the plate circuits. The grid leak and grid condenser are not used in this system in any way.
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