Radio mirror (Jan-Oct 1923)

IVIJIII1 RADIO DIGEST May 12, 1923 What Now of the Hazeltine Neutrodyne Circuit? Latest Addition to Hook-Up Family Presents Possibilities By H. J. Marx THE latest development in Radio is the popular craze for new circuits. The rankest amateur plays with his apparatus, hooks it up in a slightly different way, hears a station and promptly advertizes that he is the inventor of a new circuit. The Radio publications, hard pressed by a clamoring rank of fans for new stuff, promptly fall and announce that they are going to feature another new wonder circuit. The question of the practicability of these new circuits can only be decided through an actual set-up of the apparatus and a test of operation. Considering the number of these new wonder circuits, the reader can readily conceive the fact that it is not an inexpensive proposition. In doing this, though, the real worth of the circuit is soon disclosed. The simplicity unit, should be kept as low as possible. Because of this, the peculiar method of winding honeycomb coils was developed and in like manner lattice and spider web coils were placed on the market. This same condition holds true of transformers and even in vacuum tubes, between the tkree elements because of the dielectric value of the vacuum in the bulb. Even the wiring of the set creates capacity reactions if closely spaced. The actual microfarad value of this capacity effect may be small, but its ultimate effect on the operative efficiency of a receiving circuit is very important. Professor Hazeltine discovered a method of fighting fire with fire — namely, of applying an external capacity to the circuit from tube to tube which offsets or neutralizes the internal capacity of the coupling. or difficulty of the hook-up becomes apparent. There are many circuits that are unusually good and efficient, but perhaps are much too complicated for the average fan to construct; then, too, they are difficult to operate. Sometimes the difficulty may not necessarily be one of construction but rather a question of theoretical balance of the circuits. This last factor is one that the greatest percentage of fans will find it extremely difficult to overcome. One of the new circuits that is effected by this last factor is the Hazeltine Neutrodyne. The word "circuits" is used but actually it is a misnomer. The Hazeltine Neutrodyne is not a circuit but rather a method of overcoming, through neutralization, the various capacities in the coupling from tube to tube of any multi-tube receiving set. Theory of Neutralization Every amateur knows that the internal capacity, due to the condenser action between turns in the windings of any tuning The values of these neutralizing capacities are so small that they are expressed in units of micro-microfarads. And one million micro-microfarads make one microfarad. Expressed in microfarads the value of the neutralizing capacity runs from .000001 to .00001 microfarad. It is in this respect that the writer feels that the application of this principle to the average receiving set is a little beyond the ability of the average Radio fan. The best method of obtaining such low capacity values is by connecting two or more very small condensers in series, then the capacity value of the series becomes — C=— j ] j (depending on the num ■ 1 -.t ber in series) Ci C2 Cs Because of the low value necessary the adjustment becomes exceptionally difficult unless the proper equipment, methods and facilities are available. As a manufacturing proposition, with testing equipment available, it is a simple matter, but rare is the amateur that can boast of all this. The method used in manufacturing the Neutrodyne condensers is illustrated in the small insert. There is a small composition tubing of good dielectric value into which there is inserted copper wire at each end — the thickness will be about No. 8 gauge. Over the tube is slipped a copper sleeve. There is then a condenser capacity between the tube and the wire at each end, but since the wires are not touching or connected, the whole is equivalent to two condensers in series. By pushing the wires in or pulling them further out, a very minute control of a low capacity value is obtained. After the proper value has been reached the wires are held in position and the hole unit sealed. In other words, a permanent variable is not necessary. A Neutrodyne Hook-up In the hook-up is given a circuit in which the neutrodyne system has been incorporated. The two condensers marked C-l are the neutrodynes, the adjustment of which will be detailed later. The circuit consists of two stages of Radio frequency amplification, tube detector and two stages of audio frequency amplification, one of which is refiexed to the first Radio frequency tube. The second stage of audio uses a separate tube, making four tubes in all. Condensers C-2 should have a capacity of .001 to .002 mfd. Condensers C-3 are variable, with a capacity of .0005 mfd. One rheostat is used for the two Radio frequency tubes, one for the detector and one for the separate audio frequency tube. Depending on the type of tubes used, the plate voltage may require changing. Adjusting' the Neutralizing' Capacity The set is completely set up and tuned in for reception. In adjusting the first neutralizing condenser the wire to the filament terminal of the socket of the second tube is disconnected. This shuts out the filament current of that tube without removing it from the socket. There will still be sufficient capacity coupling to pass signals through and reception will be heard in the receivers. The first condenser is then adjusted until this reception in the receivers is completely shut off. In this way the capacity coupling has been completely neutralized. The filament wire is connected and the same way is followed for the second condenser and the third tube. After the adjustments are completed these condensers are sealed and should not be further adjusted. But any alteration in the coupling apparatus nullifies the action of the neutralizing condensers. The internal capacity of vacuum tubes of the same type does not vary to any great extent and does not necessarily require new adjustment of the neutrodyne when a tube is changed. A change in the type of tube will, however. AERIOLA SR. STYLE TUNER UNIT Green silk on Bakelite Tubes with diagram, $5.65. REINARTZ ULTRA CIR. SET PARTS, $29J# Ultra Reinartz Tuner Unit & Diag., $5.95. wound to the specifications of March 24 Badio Digest. Bub/ Mica-Copper-Bakelite mounted Condensers X. P. binding posts, .00015, 50c; .0015, 60c; .0025, 70c. Beinaru coil Doub. green silfc-Bafcelite Spider. $1.65; Be'nartz plate circuit chokes (triple adjustable), $1.70. Complete set Beinartz tuner and detector parts, $10.95. Tuner, Det. and 2 Stage. $18.90. Two stage outfit. $8.95. GOVT RADIO STORAGE BATTERIES New Signal Corps Edison 3 cell type BB-4. $4.50; Single Cells for W. D.-ll tubes. $1.50: 60 A. H. for W. D.-ll tubes. $5.25; 6 Volts Edison, $7.75; Edison "B" battery single elements, 4c ea.; double, 10c. HI-POWER AMPLIFYING TRANSFORMERS Best! Loudest! No burn-outs. $2.65 with special diagram. GENUINE PEANUT TUBES Wonderful Det. and Amplifier. Smallest tube macln (aeroplane style). 1 V., H. amp., %" dia. x 2M" long FLEWELLING .006 COND'RS & PARTS .006 Bakelite-Buby Mica-Copper Calibrated Cond., 85c. Spider coils, green silk on Bakelite, $1.75 ea, NEW SPECIALS 30 OHM BHEC for 201-A or W. D.-ll tubes, $1.00. Variable grid leaks, 1/10 to 5 Megohms, 75c. HIPOWEB LOUD SPEAKER AND PB. BALDWIN PHONES. $10.90. Variable grid. Cond., .00025 or .0003 max., 45c. Vernier Attachment for any Var. Condenser. 95c. Armstrong Super. New 3 tube outfit. Owner sa-jrificing. 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