Early vacuum-tube (referred to as "audion-bulb" in this extract) radio receivers required two separate batteries in order to operate -- an "A" Battery connected to the tube filament, and a "B" battery connected to the plate. (A few sets also required a third battery, the "C" battery, connected to the tube grid). By the mid-twenties, sets that could operate on house current began to appear, although battery operated sets continued to be common in rural areas which didn't have electrical service. The Automobile Storage Battery, O. A. Witte, 1922, pages 252-256:
The wide-awake battery man will not overlook the new and rapidly growing field which has been opened for him by the installation of hundreds of thousands of radio-phone receiving sets in all parts of the country. The so-called radio "craze" has affected every state, and every battery repairman can increase his income to a considerable extent by selling, charging, and repairing radio storage batteries.
The remarkable growth of the radio-phone has, of course, been due to the radio broadcasting stations which have been established in all parts of the country, and from which concerts, speeches, market reports, baseball reports, news reports, children's stories and religious services are sent out. These broadcasting stations have sending ranges as high as 1,000 miles. The fact that a service station is not located near a broadcasting station is therefore no reason why it should not have its share of the radio battery business, because the broadcasting stations are scattered all over the United States, and receiving sets may be made powerful enough to "pick up" the waves from at least one of the broadcasting stations.
Radio receiving sets may be divided into two general classes--the "Crystal" sets and the "Bulb" sets. "Crystal" sets use crystals of galena (lead sulphide), silicon (a crystalline form of silicon, one of the chemical elements), or carborundum (carbide of silicon) to "detect" or, in other words, to rectify the incoming radio waves so that they may be translated into sound by the telephone receivers. Receiving sets using these crystals do not use a battery, but these sets are not very sensitive, and cannot "pick up" weak waves. This means that crystal receiving sets must be used near the broadcasting stations, before the waves have been weakened by traveling any considerable distance.
As a general rule, the radio-listener's first receiving set uses a crystal detector. Very often it is difficult to obtain good results with such a set, and a more elaborate set is obtained. Moreover, even if a crystal set does give good results, the owner of such a set soon hears of friends who are able to hear concerts sent out from distance stations. This gives him the desire to be able to hear such stations also and he then buys a receiving set which uses the "audion-bulb" for detecting, or rectifying the incoming waves.
The audion-bulb resembles an ordinary incandescent lamp. It contains three elements:
1. In the center of the bulb is a short tungsten filament, the ends of which are brought out to two terminals in the base of the bulb. This filament must be heated to incandescence, and a storage battery is required for this purpose, because it is necessary to have a very steady current in order to obtain clear sounds in the receiver. Lately plans have been suggested for using a direct-current lighting line, and even an alternating current lighting line for heating the filament, but at present such plans have not been perfected, and the battery will undoubtedly continue to be used with the majority of sets.
2. Surrounding the filament but not touching it is a helix of wire, only one end of which is brought out to a terminal in the base of the bulb. This helix is called the "grid." In some bulbs the grid is not made in the form of a helix, but is made of two flat gridlike structures, one on each side of the filament.
3. Surrounding the "grid" is the "plate" which is sometimes in the shape of a hollow metallic cylinder. Some plates are not round, but may be oval, or they may be two flat plates joined together at some point, and one placed on either side of the grid. The plate has one terminal in the base of the bulb.
The action of an audion-bulb is quite complex, but a simpler explanation, though one which may not be exactly correct from a purely technical point of view, is as follows, referring to Figure 159:
The "A" battery heats the filament, causing a stream of electrically charged particles to flow out from the filament in all directions. These electrons act as a conductor, and close the circuit which consists of the plate, the "B" battery, and the telephone receivers, one end of this circuit being connected to one side of the filament circuit. Current then flows from the positive terminal of the "B" battery to the plate, then to the filament by means of the stream of electrons emitted by the filament, along one side of the filament, through the wire connected to the positive terminal of the "A" battery to the telephone receivers, through the receivers to the negative terminal of the "B" battery.
As long as the filament remains lighted a steady current flows through the above circuit. The "grid" is connected to the aerial wire to intercept the radio waves. These waves produce varying electrical charges on the grid. Since the stream of charged particles emitted by the filament must pass through the grid to reach the plate, the charges which the radio waves produce on the grid strengthen or weaken the stream of electrons emitted by the filament, and thus vary the current flowing in the telephone receiver circuit. The changes in this current cause the receiver diaphragm to vibrate, the vibrations causing sounds to be heard. Since the variation in the telephone receiver circuit is caused by electrical charges produced by the radio waves, and since the radio waves change according to the sounds made at the transmitting station; the variations in the telephone receiver current produces the same sounds that are sent out at the transmitting station. In this way concerts, speeches, etc., are reproduced in the receivers.
The modern radio receiving set includes various devices, such as variable condensers, variocouplers, loose-couplers, variometers, the purpose of which is to "tune" or adjust the receiving set to be capable of receiving the radio waves. An explanation of such devices is not within the scope of this book, but there are numerous reasonably priced books and pamphlets on the market which describes in a simple manner all the component parts of a radio receiving set.
Vesta Radio Batteries. Fig. 160 shows the 6EA Series, "A" Battery. Fig. 161 shows the V6EA Series, "A" Battery. Fig. 162 shows the R6EA (Rubber Case) Series, "A" Battery. Fig. 163 shows the "B" Battery.
From the foregoing remarks it is seen that a six-volt storage battery is required with each receiving set which uses the audion-bulb type detector. The filament current of an audion-bulb averages about one ampere. If additional bulbs are used to obtain louder sounds, each such bulb also draws one ampere from the storage battery. The standard audion-bulb receiving set does not use more than three bulbs, and hence the maximum current drawn from the battery does not exceed three amperes.
The automobile battery manufacturers have built special radio batteries which have thick plates and thick separators to give longer life. The thick plates are much stronger and more durable than the thin plates used in starting and lighting work, but do not have the heavy current capacity that the starting and lighting battery plates have. A high current capacity is, of course, not necessary for radio work, and hence thick plates are used.
Batteries used for radio work do not operate under the severe conditions which exist on automobiles, and trouble is much less likely to develop. However, the owner of the radio set rarely has any means of keeping his battery charged, and his battery gradually discharges and must then be recharged. It is in the sale of batteries for radio work and in the recharging of them that the battery man can "cash-in" on the radio phone "craze."
This business rightfully belongs to the automobile battery man and he should go after it as hard as he can. A little advertising by the service station man, stating that he sells radio batteries, and also recharges them should bring in very profitable business. The battery man who calls for and delivers the radio batteries which need recharging and leaves rental batteries in their place so that there is no interruption in the reception of the evening concerts is the one who will get the business.
As already stated, radio storage batteries have thick plates and thick separators. Perforated rubber sheets are also used in addition to the separators. Large sediment spaces are also generally provided to allow a considerable amount of sediment to accumulate without causing short-circuits. The cases are made of wood or hard rubber. Since radio batteries are used in homes and are, therefore, used with handsomely finished cabinets containing the radio apparatus, the manufacturers give the cases of some of their radio batteries a pleasing varnished or mahogany finish. Before returning radio batteries which have been recharged, the entire batteries should be cleaned and the cases polished. Returning radio batteries in a dirty condition, when they were received clean, and polished, will drive the radio recharging business to some other service station.
VESTA RADIO BATTERIES.
The Vesta Battery Corporation manufacturers three special types of "A" batteries for radio work, as follows:
1. The 6EA battery, made in capacities of 60, 80, and 100 ampere hours. Fig. 160.
2. The V6EA7 battery, having a capacity of 80 ampere hours. Fig. 161.
3. The R6EA battery, having a capacity of 100 ampere hours. Fig. 162.
These batteries have 5, 7, 9 plates per cell, respectively. The plates are each 5 inches high, 5 7/8 inches wide, and 5/32 inches thick. The cases for these batteries are furnished in three designs--plain black boxes (all sizes), finished maple boxes (7 plate size only), and hard rubber boxes (9 plate size only). These Vesta batteries are the "A" batteries used for heating the filaments of the audion bulbs. The Vesta Radio "B" battery, Fig. 163, is a 12 cell, 24 volt battery, with a 22 and a 20 volt tap.