Figure 10.1. This is a direct screen capture of the LT spice schematic page. There are several lines of text on the screen as follows. To be sure that you understand where one leaves off and another begins they will be separated by the word next. Dot op, next, dot ac dec 100 1 1meg, next, dot lib 12AX7 dot sub, next, dot lib 12AU7 dot sub, next, dot lib 6AU6 dot sub. These mysterious fragments of text will become familiar if you learn spice. It is possible for the blind to use P Spice. Lessons on how to use LT spice for the sighted and P Spice for the blind will be posted sooner rather than later. And now, back to our story. There is a generator on the left labeled V 1 AC 1. The lower end is grounded.

There are two independent amplifiers on this schematic. Just as a breadboard can hold two amplifiers for comparison a spice simulation can hold two amplifiers for comparison. Triode amplifier. The upper end of the generator connects to the grid of a 12 A X 7. The cathode goes to ground through the parallel combination of a 3.9 k ohm resistor and a 47 u f capacitor. The plate of the 12 A X 7 goes through a 750 k ohm resistor to plus 250 volts. The plate of the 12 A X 7 connects directly to the grid of a 12 A U 7. The plate goes directly to plus 250 volts. The cathode of the 12 A U 7 goes through a 33 k ohm resistor to ground. The cathode also goes to a point labeled out, T.

Pentode amplifier. The upper end of the generator labeled V1 A C 1, also goes to the control grid of a 6 A U 6. The cathode goes to ground through the parallel combination of a 1.2 k ohm resistor and a 150 u f capacitor. The screen grid of the 6 A U 6 goes through a 680 k ohm resistor to plus 250 volts. There is a 3.3 u f capacitor connected from the screen grid to the cathode, not ground. See text. The suppressor grid is connected to the cathode. Note, it appears to be common practice not to show suppressor grids on spice schematics. Their existence and connection is taken as a given. The plate goes through a 270 k ohm resistor to plus 250 volts. The plate also goes directly to the grid of another 12 A U 7 triode. The plate of this triode goes directly to plus 250 volts. The cathode goes to ground through a 33 k ohm resistor. The cathode also goes to a point labeled out, P. On the right side of the schematic is another generator labeled V2 250. The lower end is grounded and the upper end connects to plus 250 volts.

End verbal description.
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