The Birmingham age-herald., 1922-07-09
First Aid For Radio Fans
MaterinI for Ar.nstrong Set

regeneratiYe circuit. VIII you please therefore advise me what type of co mmercial products will answer for the following or whether they can be readily assembled at home. If 1t is possible to make them, will you please describe the method and the
 materials necessary? l. Two 12,- o00-ohm resistance coils (these are used on the plate circuit between the intermediate tube and primary of the transformer). 2. One 5-rnilli
 henry air core choke coil. 8. One l henry iron core choke coil. 4. I should like to know whether pair of 3,O00-ohm telephone receivers can he used to hear this circuit or wheth- CT it is necessary to use power loud speaker. 5. Do you think the "Aeriola" oxide filament ~4h volt ar-plifier tubes would function well with this apparatus? If so, can you tell me whether these tubes will fit In the standard tube socket7 J. M. H.
 X. The two 12,OOO ohm resistance coils in Major Armstrong's super regenerative circuit consist of Lavite resistances, which of course, are of non-inductive character. These re- sistance wire. giving that total value sistances are made of special com position. It is not necessary. how ever, to use that particular type. The same purpose may be achieved by the use of any resistance wire, giving that total value of resistance. prb- vided that the coils are wound in a non-inductive manner. 1. The way in which this is done Is to take the requisite amount of wire necessary to give 12,000 ohms and then double it in half. Take the loop end of the wire so doubled and wind it around some suitable insu- latng form. The two free ends will then come together and form the ter of the resistance coll. The current then flowing through this coil will flow in one direction half way through the coil, and in the op- posite direction through ethe other half; thus, neutralizing any inductive effect that might occur in the coil Itself. 2. The open core choke coil of ten milli-henries inductance can be any type of coil that has that total amount of inductance in 1t. The honey comb coil, for instance, with that quality of inductance can be used. 8, The iron core choke coil of 100 mill llihenries inductance Is the regulation type of choke used in or dirary telephone filter circuits. and If you cannot obtain 1t at a radio store I do not think that you will have any difficulty in getting one at stores which make a practice of sell
 Ing telephone installation, equip ment. If you use pair of 5000 ohm telephones in the circuit, l am afraid that the amount of current flowing through the coils will be too large for them, and unless they are very rigidly constructed you will get a tremendous amount of vibra- ton. What 1 would suggest is the telephone receiver of the type which uses a mica diaphragm actuated by a balance armature. A power loud speaker is not necessary with this set, as you get all of the power from amplification from the super itself. The Aeriola OK idle filament AZ volt tubes may all right with this set, ,,pro- vded that they are hard" tubes. I am under the impression that they are not altogether hard. In any case they will, not fit the standard vacu- um tube socket. You will have to get an adapter, or a special socket for them.
 Notes on Same Credit
 0. Will you please give me the following information regarding the uper-regenerative receiver; l. Can better results be obtained by using an outside aerial instead of the in door loop aerial? 2. Are transform CTS used with bulbs? 3. Can ordi- nary variometer and variocouplers
 ~, A,@II. otx volt storage battery be used on all three tubes to light the filamentf 3. Can "B" batteries be used on the plates of all three tubes, and If so what, should the voltage be? 6. phones? '. Is there another ground in the circuit other than aerial? c. E. M.
 A. 1. An aerial must not be used with this system for two reasons; first, if an aerial Is used too much energy will be picked up and as a result of the tremendous amplifica- ion which the system gives. the whole set will be paralyzed; and second. if you use an aerial, there will be tremendous amount of 's diation and you will interfere with practically every other set in lour immedite vicinity. 2. An audto- Frequency transformer Is used be- lore the third tube. This tube, of course, is the regular amplifier tube, similar to any one-step ampli- fer in the ordinary system. This transformer can be of any standard make. 3. An ordinary varia-coupier ,an be used for the tuning circuit and tickler coil. In this case the primary of the vario-coupler really becomes the secondary oscillating circuit of the entire system. and the -otcr of the coupler becomes the
 t necessary to double the number of turns on the rotor when using the standard vario-coupler. 4. A 6-vult storage pottery can be used as an "A" battery, which will be common for all three tubes. 5. "B" batteries are used on tho plate circuit of all three tubes, with 90 volts each oa the first two tubes and 200 volts on the third tube. 6. The voltage used in the telephone circuit Is 200 volts, stated above. This is obtained by using a separate "B" battery of 1io volts and then connecting it in series to the 90-volt battery used on the other two tubes. The nega- tive lead of the 110-volt battery is attached to the positive terminal of the 90-volt battery. '. Since the loop aerial is used with this set, 1t
 IS not necessary to have the ground at all. although of course, you can follow the practice of some in connection with
 oop aerials by grounding one sice of the loop. If you do this, the loop than becomes absolutely uni -direc- tional and can only receive signals when one of its edges is pointed to- ward the station from which you desire to receive. If you turn the loop completely around, so that the opposite edge is pointing toward the station, you will not get signals at all, because of the uni-direct1onai effect that a grounded loop has.
 and inc transnnifter takes the sound,