Radio Batteries
There may be confusion in the minds of some as to batteries so a classification of types and functions will be helpful, particularly to the novice.
Radio batteries may be classified according to the three elements of the vacuum tube which they serve, as
"A" battery "B" battery "C" battery
The three elements of the common vacuum tube, filament, plate and'grid are often designated by the letters A,.B and C.
The order in which the letters are assigned corresponds to the historical development of the tube.
The heated filament is comparatively an old device and the battery which lights it is known as the filament battery or "A" battery.
The plate was the second element to be invented and any battery used in the plate circuit is a "B" battery.
A later invention is the grid and the battery in the grid circuit is termed a "C" battery.
The B battery, connected in the plate circuit, maintains the plate at proper pressure and supplies the energy which operates the head phones or loud speaker.
The. length 6f the period of satisfactory results, however, depends upon the quality of the battery. No battery can give out more than is put into it. That is why extreme care should be taken in the selection of B batteries,' in order to secure the best results possible from radio. All B batteries of standard makes when fresh will measure up to the required voltage and give equal results at the start, but the initial voltage does not indicate the length of its useful life, which in a 45 volt battery ends after it drops below 34 volts.
- FILAMENT
PLATE.
Fig. 1 -—Hydrostatic analogy illustrating function of the grid. Consider a U tube at the bottom center of which is placed a pet cock and in one side of which with the pet cock closed is placed a quantity of mercury. If this pet cock be opened wide, the mercury will immediately seek its own level, that is, the same amount of mercury by weight will flow up into the other side*of the U tube; and after oscillating for a few moments in an attempt to seek a level, it will come to rest. In the case of the "vacuum tube, the flow of this mercury which is the electron flow from the filament is controlled by means of the grid which is the pet cock at the bottom of the U tube, to the plate which is the other side of the U tube.
NOTE.—The discrim inatinp radio set purchaser is primarily interested in tone quality that is, the undistorted reproduction Of the voice or .instrumental music. Many factors govern tone quality. The tare used in the adjustment of the transmitting apparatus at the broadcast station and the scientific placement of the pick up microphone, as related to the acoustical properties in the studio have a direct bearing on the tone quality of the broadcast program. The engineering design of the receiving set, together with the care used in its construction, are factors of considerable importance. The proper selection of the parts entering into the set; the scientific balance between the related parts are equally important.
A Battery.
This battery performs one specific function, that of heating the filament in the vacuum tube. If, for any reason this A battery be low in voltage, there will be a consequent low rate of electron emissions and the receiving set will not operate satisfactorily.
This battery performs two specific functions in a receiving set. It insures a positive pressure on the plate of the tube to which the negative electrons which are emitted from the filament may flow and improves the quality of reception.
C Battery.
This battery functions as a governor on the grid or control device to retard or accelerate the flow of electrons from the filament to the plate. By so doing, the C battery permits a correct volume of electrons to flow from filament to plate thus controlling the plate current which flows from plate to filament and allows the tube to be operated on the straight portion of the curve which insures quality reception.
Testing Radio Batteries.—Much of the service life of dry cell B batteries in radio receiving sets depends on the conditions of use together with the type and number of tubes.
The term service hours is the total time that a battery will deliver the necessary current before it must be discarded from the set as being no longer useful. High service hours are, therefore, necessary for economical operation. Service hour tests are made by discharging batteries under various conditions, usually through a constant resistance or at a constant current rate.1 The latter test is made by maintaining a constant current in the battery by means of an adjustable resistance. This type of test can be either continuous or intermittent with periods of rest between discharges.
The intermittent test represents the service of a battery under usual broadcast listening use.
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Milliamperes Current Fig. 2.—Diagram of service hours at various currents from tests made on Burgess dry batteries. Discharge based on intermittent service of 2 hours per day to an end voltage of 17 volts for a 22 H volt battery. Milliamperes Current Fig. 2.—Diagram of service hours at various currents from tests made on Burgess dry batteries. Discharge based on intermittent service of 2 hours per day to an end voltage of 17 volts for a 22 H volt battery. To determine the expected service hours of a B battery, it is only necessary to determine the average current drain on the battery and then pick off the service hours from curves fig. 2. In a receiving set however, it is almost impossible to estimate the plate current accurately as it is affected by the various opnstants of the receiving set itself. The. only correct way to determine this current is by measuring it with a milli-am-meter, and this method is recommended not only to determine the battery drain but as a means of checking the installation in the receiving set and of adjusting the Various tube voltages. The milli-ammeter offers a convenient method of testing the plate and grid battery conditions as well as checking the current drain of the set. When strong signals are received with the set, there should not be a fluctuation of the milli-ammeter pointer. A noticeable fluctuation indicates 
Fig. 3.—Weston plate or grid milli-ammeter for measuring the plate current of vacuum tubes. It will give a deflection for steady or pulsating direct current and will indicate the average value of a pulsating current. Superimposed upon the steady plate current is the current due to the modulation which is an alternating current and will cause the total plate current to be a pulsating current varying at the same frequency as the modulation current. The milli-ammeter will again indicate the average value ol this current and if the tube be working at a point where it rectifies, this average value will not be the same as the value of the unmodulated steady plate current and therefore fluctuate with the modulation. For perfect repro-. duction, amplifying tubes should not rectify and no variation in the indication of the milli-ammeter Should occur. In practice however, on account of the properties of vacuum tubes, some rectification will result, but by properly adjusting the grid bias, a minimum fluctua-tion in the plate current may be obtained consistent with good quality and volume. Fig. 3.—Weston plate or grid milli-ammeter for measuring the plate current of vacuum tubes. It will give a deflection for steady or pulsating direct current and will indicate the average value of a pulsating current. Superimposed upon the steady plate current is the current due to the modulation which is an alternating current and will cause the total plate current to be a pulsating current varying at the same frequency as the modulation current. The milli-ammeter will again indicate the average value ol this current and if the tube be working at a point where it rectifies, this average value will not be the same as the value of the unmodulated steady plate current and therefore fluctuate with the modulation. For perfect repro-. duction, amplifying tubes should not rectify and no variation in the indication of the milli-ammeter Should occur. In practice however, on account of the properties of vacuum tubes, some rectification will result, but by properly adjusting the grid bias, a minimum fluctua-tion in the plate current may be obtained consistent with good quality and volume.
improper B or C battery voltages or both. When the C battery voltage is too low there will be a fluctuation of the needle toward zero with strong signals. In case the milli-ammeter hand vary up the scale, too low a B battery voltage is indicated. Erratic fluctuations indicate too low.B and C battery voltages. The current at the installation of new batteries with a high voltage will be higher than the average current. Experience shows that the average current is about 15% lower than the initial current. For example if the initial current be 20 milli-amperes, the average can be estimated as being 17 milli-amperes. This figure then, is used to determine the approximate service hours from the curves, fig. 2. Either a hydrometer or a volt meter or both together may be used to test storage batteries. The hydrometer gives an indication of the specific gravity or unit weight of the acid solution in the battery. The specific gravity gives a good indication of the charge in the battery.
The following instructions are given by Westinghouse for hydrometer and volt meter tests: A Batteries.—A hydrometer reading of 1.285* indicates a fully charged battery; 1.100 indicates a discharged battery. B Batteries.—Small special B battery hydrometers are now obtainable and their use is entirely satisfactory. B batteries are charged and discharged at the gravities given in the accompanying specific gravity table. Do not take a hydrometer reading immediately after adding distilled water to the battery. Such a reading would be incorrect as the water will float on the acid solution. No accurate reading can be obtained until charging has mixed the water with the acid. The hydrometer reading will be a correct indication of the battery charge so long as none of the acid is spilled and occasional overcharges are given. Be sure to replace the acid in the same cell it was taken from for test. *NOTE.—Occasionally during the life of a battery, a cell may read as low as 1.260 instead of 1.285. No harm will be done if the cell do not continue to decrease in gravity. Different gravities are used to obtain different results. Where a compact battery is desired acid space is limited and a high gravity solution (that is one having a high percentage of sulphuric acid) must be used to obtain the required capacity Where there is plenty of space and the current requirements are moderate a lower gravity acid is used. The table on page 91 gives the specific gravity of different types of batteries at charge and discharge. Never add acid or any other substance or solution to the battery, except distilled water. Recharge batteries as soon as they have reached the discharge points given previously. Do not allow batteries to stand in a discharged condition. About every fourth charge the batteries should
be given an overcharge by leaving them on for two or three hours longer than necessary. This will insure keeping the plates in such condition as-will enable them to give a maximum of capacity. If only alternating current be available, a rectifier of some kind to change the alternating current into direct current for charging the battery must be used. Volt meter Test.—The individual cells of any radio battery! may be tested by means of a volt meter having a scale reading from 0 to 3. A Batteries.—The cells are discharged when the voltage drops to 1.8 wl)ile the battery is being used at a normal rate. The cells are fully charged when the voltage averages from 2.4 to 2.6 for a period of several hours while the battery is on the charging line at the finish charge rate. B Batteries.—The B batteries should be immediately recharged when 
Fjg.. 6.— Willard A power unit and B battery charger. It is a combined trickle charger ana conventional radio battery charger with a two ampere rate available. This two ampere rate is held in reserve until such time as it is necessary to compensate for any excessive use of the receiving set. The battery has visible gravity balls and whenever it is found that the green ball shows a tendency to sink, the high charge rate should be reso'ted to until the battery again come? back to a normal condi Lion. The balance of the time, of course, the unit will be used as a straight trickle charger. A double partition is placed between the batter^ and charger compartments The charger is of the bulb type. Fjg.. 6.— Willard A power unit and B battery charger. It is a combined trickle charger ana conventional radio battery charger with a two ampere rate available. This two ampere rate is held in reserve until such time as it is necessary to compensate for any excessive use of the receiving set. The battery has visible gravity balls and whenever it is found that the green ball shows a tendency to sink, the high charge rate should be reso'ted to until the battery again come? back to a normal condi Lion. The balance of the time, of course, the unit will be used as a straight trickle charger. A double partition is placed between the batter^ and charger compartments The charger is of the bulb type. any cell in the battery has dropped below 2 volts. The cells should be kept on the charging line until the voltage of the cells averages from 2.4 to 2.6 for a period of several hours. Note carefully that voltage readings to determine discharge should be taken while the batteries are being used with the radio set at a normal rate of discharge. Also note that voltage taken to indicate a charged condition is taken while the battery is on the charging line either at its normal rate of charge or at the finish rate if such be recommended. A 6 volt battery is not charged when it reads 6 volts and a 24 volt battery is not charged when it reads 24 volts. A cell in good condition will show 2.1 volts in a few minutes after being put on the charging line and some cells may show an even higher voltage. Thus a 3 cell battery would show' over 6 volts and a 12 cell battery would show over 24 volts'within a few minutes after being placed on charge. A 6 volt battery should not be taken off the charging line until it shows about 7.5 volts and a 12 cell battery should be charged until it shows about SO volts. If a 6 volt battery be taken off the line at a voltage of 7.5 volts and allowed to stand idle for several 
Figs. 7 and 8.—Willard B power unit. The rectifying units consist of 4 jars containing the electrodes. The rectifier is not the conventional lead aluminum ty pe but has one aluminum and one special electrode in each of the four jars. This special electrode material prevents delay before going into action that is found where the aluminum lead type of rectifier is used. Variable voltage taps for the detector and amplifier allow close regulation and insure maximum results from the receiving set. There is a fixed resistance inside of the power unit, held in fuse clips that looks very similar to a cartridge fuse. This, however, is a special resistor and should not be replaced. Figs. 7 and 8.—Willard B power unit. The rectifying units consist of 4 jars containing the electrodes. The rectifier is not the conventional lead aluminum ty pe but has one aluminum and one special electrode in each of the four jars. This special electrode material prevents delay before going into action that is found where the aluminum lead type of rectifier is used. Variable voltage taps for the detector and amplifier allow close regulation and insure maximum results from the receiving set. There is a fixed resistance inside of the power unit, held in fuse clips that looks very similar to a cartridge fuse. This, however, is a special resistor and should not be replaced. hours it will show a reading of about 6.3 volts, this is not due to any loss of charge or any trouble in the cell, but to the escape of gas from the cell and is a normal process. The voltage of the cell will then gradually decrease from 2.1 to 1.8 as the battery is discharged through use. It is necessary to watch the voltage on B batteries more closely than on the A batteries. The amount that the voltage of a cell drops depends upon the quantity of current flowing and the resistance of the circuit through which it flows. The amount of current drawn from a B battery is small and not enough in itself to produce much of a voltage drop. The drop in voltage is due rather to the exhaustion of the plate than to the current flow. The result is that a cell that reads 2 volts to-day may read only 1 volt to-morrow due to the absolute exhaustion of the plates. The voltage of individual cells of the battery should be tested at frequent Fig. 9.—Diagram showing method of charging Universal battery from alternating current with Universal chemical rectifier; connect B battery chemical rectifier and lamp as shown. The rectifier must be properly prepared for service by being filled with the chemical solution before connecting. From 110 volt lines, one or two 24 volt batteries can be charged from one lamp by connecting the batteries in series (positive of one to the negative of the next). Use only a 25 watt lamp. For 24 volts this gives a charging rate of .083 ampere; for 48 volts it gives a charging rate of .05 ampere. intervals and the battery recharged if one or more cells be much lower than the rest. In using a volt meter care must be taken to procure an accurate instrument. 
Fig. 9.—Diagram showing method of charging Universal battery from alternating current with Universal chemical rectifier; connect B battery chemical rectifier and lamp as shown. The rectifier must be properly prepared for service by being filled with the chemical solution before connecting. From 110 volt lines, one or two 24 volt batteries can be charged from one lamp by connecting the batteries in series (positive of one to the negative of the next). Use only a 25 watt lamp. For 24 volts this gives a charging rate of .083 ampere; for 48 volts it gives a charging rate of .05 ampere. Charging Radio Storage Batteries—A battery is not 100% efficient, and so in charging it is necessary to put about one | |||||||||||||||||
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