As you will see from A in Fig. 51 it has three taps. The two taps which are connected with the ends of the resistance coil are shunted around the A battery and the third tap, which is attached to the movable contact arm, is connected with the B battery tap, see B, at which this battery gives 18 volts. Since the A battery gives 6 volts you can vary the potential of the plate from 18 to 24 volts. The potentiometer must never be shunted around the B battery or the latter will soon run down. A potentiometer costs a couple of dollars.
The Parts and How to Connect Them Up.--For this regenerative set you will need: (1) a honeycomb or other compact three-coil tuner, (2) two variable (.001 and .0005 mfd.) condensers; (3) a .00025 mfd. fixed condenser; (4) a 1/2 to 2 megohm grid leak; (5) a tube detector; (6) a 6 volt A battery; (7) a rheostat; (8) a potentiometer; (9) an 18 or 20 volt B battery; (10) a fixed condenser of .001 mfd. fixed condenser; and (11) a pair of 2000 ohm head phones.
To wire up the parts connect the leading-in wire of the aerial with the primary coil, which is the middle one of the tuner, and connect the other terminal with the ground. Connect the ends of the secondary coil, which is the middle one, with the posts of the variable condenser and connect one of the posts of the latter with one post of the fixed .00025 mfd. condenser and the other post of this with the grid; then shunt the grid leak around it. Next connect the other post of the variable condenser to the - or negative electrode of the A battery; the + or positive electrode of this to one terminal of the detector filament and the other end of the latter to the electrode of the A battery.
Now connect one end of the tickler coil with the detector plate and the other post to the fixed .001 mfd. condenser, then the other end of this to the positive or carbon pole of the B battery.
This done shunt the potentiometer around the A battery and run a wire from the movable contact of it (the potentiometer) over to the 18 volt tap, (see B, Fig. 51), of the B battery. Finally, shunt the head phones and the .001 mfd. fixed condenser and you are ready to try out conclusions.
A Regenerative Audio Frequency Amplifier Receiving Set.--The use of amateur regenerative cascade audio frequency receiving sets is getting to be quite common. To get the greatest amplification possible with amplifying tubes you have to keep a negative potential on the grids. You can, however, get very good results without any special charging arrangement by simply connecting one post of the rheostat with the negative terminal of the filament and connecting the low potential end of the secondary of the tuning coil with the - or negative electrode of the A battery. This scheme will give the grids a negative bias of about 1 volt. You do not need to bother about these added factors that make for high efficiency until after you have got your receiving set in working order and understand all about it.
The Parts and How to Connect Them Up.--Exactly the same parts are needed for this set as the one described above, but in addition you will want: (1) two more rheostats; (2) two more sets of B 22-1/2 volt batteries; (3) two amplifier tubes, and (4) two audio frequency transformers as described in [Chapter IX] and pictured at A in Fig. 46.
To wire up the parts begin by connecting the leading-in wire to one end of the primary of the tuning coil and then connect the other end of the coil with the ground. A variable condenser of .001 mfd. capacitance can be connected in the ground wire, as shown in Fig. 52, to good advantage although it is not absolutely needed. Now connect one end of the secondary coil to one post of a .001 mfd. variable condenser and the other end of the secondary to the other post of the condenser.
