Figure 4B.7. On the left is an air core transformer labeled antenna coil. The lower end of the primary connects to earth ground and circuit ground. The upper end of the primary connects to an antenna. The lower end of the secondary goes to ground through a 0.01 u f capacitor. The lower end also goes to a point labeled A G C. The top of the secondary goes to the top of a variable capacitor. The bottom end is grounded. The top of the secondary also goes to the third grid, pin 8, of a 12SA7 heptode tube. The cathode of the tube, pin 6, goes to the tap on the oscillator coil. The bottom of the oscillator coil is grounded. The top of the coil goes to one side of a variable capacitor, the other side is grounded. This capacitor is ganged with the one on the antenna coil. The top of the oscillator coil goes through a 220 pf capacitor to grid 1, pin 5 of the tube. Pin 5 goes through a 27 k ohm resistor to ground. Grids 2 and 4 are tied together inside the tube and come out to pin 4. Pin 4 goes through a 0.1 u f cap to ground. Pin 4 goes through a 1 k ohm resistor to plus 125 volts. Pin 4 also goes to the bottom of the primary of the I F transformer. The top of the primary goes to the plate, pin 3 of the tube. The suppressor grid and metal envelope of the tube come out to pin 1, this pin is grounded. The bottom of the secondary of the I F transformer goes through a 0.01 U f cap to ground. The bottom of the secondary also goes to the A G C point. The top of the secondary is labeled to grid of I F tube. End of verbal description.