Radio Broadcast (May-Oct 1926)

260 RADIO BROADCAST ADVERTISER ASK . ANY . . RADIO . . ENGINEER An every-night adventure of Burgess Radio Batteries One of the reasons why you should always buy Burgess Radio Batteries is that the batteries used by air' mail pilots— battleships— explorers—and the majority of recognized radio engineers— are evolved in the Burgess Laboratories and manufac tured in the Burgess factory. These batteries are identi' cal with the batteries sold by your dealer and thousands of other good dealers every where. Burgess Battery Company General Sales Office: Chicago Canadian Factories and Offices: Niagara Falls and Winnipeg No. 11 Radio Broadcast Laboratory Information Sheet The UX*2O0-A Tube July, 1926 A STABLE SOFT DETECTOR TUBE A NEW detector tube, manufactured by the Radio Corporation of America, has recently been placed on the market. It is called the ux200-A, and insofar as its operation is concerned, it is similar to the old uv-200, since its efficiency as a detector depends upon the presence of a gas in the tube. The major difference in appearance between this new tube and the ux-201-A, is the absence of the silver coating on the bulb. The UX-200-A has a bluish smoky color due to the special gas content. The characteristics of this new tube, as given by the manufacturers, are as follows: Design Same as standard UX-201-A Base Same as standard ux-201-A Filament Voltage 5 Volts Filament Current 0.25 Amperes Plate Voltage 45 Volts Maximum Plate Current 2.0 Milliamperes Plate Impedance 28,000 Ohms Grid Leak 2.0 Megohms Grid Condenser 0.00025 Microfarad It might be of interest if the action of a gas-filled detector tube is reviewed, and an attempt made to show why such a tube can be made very sensitive for detecting signals. The gas contained in the tube is composed of innumerable atoms, each of which consists of a nucleus surrounded by electrons, which are negatively charged. Normally, the positive charge on the nucleus exactly equals the negative charges on the electrons, and the atom is in a stable condition. When the filament is heated, it emits a great many electrons which are projected from its surface at very high speed. As they pass through the space between the filament and the plate, they frequently collide with some of the gas atoms, disrupting them and causing one or more of the negative electrons to be torn away from the atom, leaving what is called an ion, which is an atom that has lost one or more of its negative electrons. As soon as the negative electron is separated from its atom, it moves toward the positively charged plate with the other electrons emitted from the filament, and the plate current is thereby increased. Now, this breaking down of the atoms is called ionization, and it usually occurs at some particular value of grid and plate voltage. At the point of ionization, large changes in plate current occur with only small changes in grid potential, and if the tube can be operated at this point on the plate current curve, it will be very sensitive. In the old style uv-200 tube, the various voltages required very accurate adjustment in order to make the tube operate at the critical point of the characteristic, and this fact more or less detracted from its increased sensitivity. With a UV-201-A tube, however, very stable operation can be obtained over a wide range of voltages. As with the uv-200, operation of the UV-200-A is accompanied by a slight hiss, not unlike escaping steam, but it is not sufficiently loud to become bothersome. No. 12 Radio Broadcast Laboratory Information Sheet July, 1926 The UX-171 Tube '"THESE data on the new ux-171 tube show the important constants for this tube under various operating conditions. It is designed to handle relatively large amounts of input voltage and to deliver, with a low plate voltage, relatively large amounts of undistorted power. The table below shows the amount of power that can be delivered by the ux-171 under various input voltage conditions. This new tube will provide undistorted power handle the input with 135 volts on the plate. Its power output under the above input conditions will be below that of the ux-210. As a matter of fact, the ux-210will deliver 1.08 watts while the ux-171 will deliver .3 watts under these conditions. This latter figure, however, is more than sufficient for all normal conditions. It must be remembered that greater input voltages are required to secure greater output power. Filament current Plate current Plate impedance Amplification constant Mutual Conductance Plate voltage Grid voltage Power output in watts .5 amp 13.4 mils. 2200 ohms 2.65 1200 micromhos 90 -16.5 .1 .5 amp. 16 .5 mils. 2200 ohms 2.65 1200 micromhos 135 -27 .3 .5 amp. 20 mils. 2250 ohms 2.65 1180 micromhos 157.5 -33 .486 .5 amp. 21 .5 mils. 2325 ohms 2.7 1163 micromhos 180 ^10.5 .64 to a loud speaker in considerable volume without the use of high plate voltages. It is to be compared with theux-112 and the ux-210 tubes. The ux-112 requires 135 volts plate battery to handle input voltages of 9 volts, and under these conditions will deliver a maximum of .12 watts of undistorted power. The ux-171, however, with only 90 volts on the plate, will handle input voltages up to 16.5, and will deliver approximately the same amount of power to a loud speaker. With input voltages of 27, the ux-210 requires a plate battery of 350 volts, while the ux-171 will There are few radio receivers that will deliver 27 volts to the grid of the last amplifier tube without more amplification (an additional stage), and without taking care of overloading all along the line of low frequency amplification. The low impedance, 2000 ohms, of this tube, recommends it for use in high quality amplifiers. This is considerably below the impedance of loud speakers now on the market, which will tend to bring up the low notes. For these reasons, it will be wise to use an output transformer, as the manufacturer's circular recommends. No. 13 Radio Broadcast Laboratory Information Sheet July, 1926 Charging Storage Batteries on Direct Current NECESSARY RESISTANCES, ETC. TF ONE has a convenient source of direct current, it is a comparatively simple matter to charge storage batteries. Although such charging will necessarily be done rather wastefully, it will nevertheless be cheaper and much more convenient than having it done at a charging station. The charging may be accomplished by either of the two methods illustrated in the diagram. In A, the charging rate is determined by the value of the resistance R. Most of the power companies supply 110 to 120 volts, and for this line voltage, the following values of resistance should be used. The values are approximate and based on an average voltage of about 115. CHARGING RESISTANCE POWER DISSIPATED RATE IN RESISTANCE 1 Amp. 110 Ohms 110 Watts 2 Amps. 55 " 220 " 3 " 37 " 330 " 4 " 28 " 440 " 5 " 22 ". 550 " The last column is given so that if a resistance unit is purchased care can be taken in choosing one that is capable of dissipating the power given in the table. In place of (he resistance units we can substitute a bank of electric lights as is illustrated at L, in B. The charging rate will be determined by the total wattage of the entire bank of lamps, and this total will equal the sum of the individual watlages of the lamps. If five 40-walt lamps are used, the total will be 200 watts. If the bank consisted of one 40-watt lamp, one 150-watt lamp, and one 60-watt lamp, the total would be 40+150+60 = 250 watts. By reference to the table, the total power (wattage I required, for any value of charging rate, can be found in the last column. There are several precautions to be taken. In the first place, be sure to connect the positive side of the line to the positive side of the battery. If the batt e r y is wrongly conn ected j+-,| storage in the cir^| Battery cuit> it js likely that itwill be seriously damaged. Secondly, be sure'that none of the leads touch any metal surfaces, such as water pipes, for if this occurred a short-circuit might result. Thirdly, be certain that the charging rate is not too high. Information regarding this is generally given on the name plate of the battery. However, if this information is lacking, the charging rate should be determined by the heating of the electrolyte. As the battery charges, the temperature of the solution gradually increases, and no damage will result if the temperature is not allowed to exceed 110 degrees Fahrenheit. ★ Tested and approved by Radio Broadcast -fc