Potential 10 band equalizer. The input goes through a 33 k ohm resistor to the grid, pin 2 of a 12 eh X 7. The output connects through another 33 k ohm resistor to the other grid, pin 7 of the same tube. Each grid goes through its own 470 k ohm resistor to ground. The two cathodes, pins 3 and 8, are tied together and go through a 110 k ohm resistor to minus 150 volts. Each plate, pins 1 and 6, goes through its own 100 k ohm resistor to plus 150 volts. The second plate, pin 6, goes to the grid, pin 2 of another 12 eh X 7. The plate of this tube goes to plus 150 volts. The cathode goes through a 100 k ohm res to minus 150 volts. The cathode also goes through a 1 u f cap to the output terminal. Returning to the first tube, there is a long line extending outward to the right from pin 7, grid. There is a line from the other grid, pin 2, that goes downward and to the right under the tube symbol. This line extends as far right as the line from pin 7. There are 3 pots between the two lines. The top of each pot connects to the upper line from pin 7. The bottom of each pot connects to the lower line from pin 2. Each wiper will be described individually. The wiper of the left pot goes through a 0.18 uf cap then another 0.18 uf cap to the grid, pin 7, of another 12 eh X 7. The grid goes to ground through a 100 k ohm res. The plate, pin 6 goes to plus 150 volts. The cathode, pin 8, goes through a 120 k ohm res to minus 150 volts. The cathode goes through a 10 k ohm resistor to the junction of the two 0.18 uf caps. The wiper of the middle pot goes through a 0.0022 uf cap then another 0.0022 uf cap to the grid, pin 2 of the same 12 eh X 7. As in the other tube the grid goes to ground through a 100 k ohm res. The plate and cathode are connected the same as in the previously described tube. The 10 k ohm res from the cathode, pin 3, goes to the junction of the two 0.0022 uf caps. The wiper of the right hand pot goes through a 270 pf cap then another 270 pf cap to the grid, pin 7, of another 12 eh X 7. All other connections are as previously described. The writer believes that there are supposed to be 7 more circuits with two capacitors, 3 resistors, and a triode, to make up a 10 band equalizer. End verbal description.
Go back.