Sine wave oscillator circuit. Transistors Q1 and Q2 have their emitters tied together and they go to ground through a 56 k ohm resistor. The base of Q1 is connected through a 4.7 k ohm resistor to the base of Q2. We will return to the base of Q1 later. The collector of Q1 goes through a 1.1 k ohm resistor to plus 43 volts. The collector of Q2 goes through a 10 k ohm resistor to plus 43 volts. Q1 and Q2 are both NPN transistors. The collector of Q2 goes to the base of Q3 which is a PNP transistor. The emitter of Q3 goes through a 150 ohm resistor to plus 43 volts. The collector of Q3 goes to the anode of a diode, D1. The cathode of D1 goes to the anode of D2. The cathode of D2 goes through a 10 k ohm resistor to ground. A modification has been indicated here. The line from the 10 k resistor to ground has been exed out. Also the junction of D2 and the 10 k is marked as point X. The collector of Q3 also connects to the base of Q4, an NPN transistor. The junction of D2 and the 10 k resistor goes to the base of Q5, a PNP transistor. The collector of Q4 goes to plus 43 volts. The emitter of Q4 goes through a 15 ohm resistor then another 15 ohm resistor to the emitter of Q5. The collector of Q5 is grounded. The junction of the two 15 ohm resistors is the output of the gain block and connects to a number of different places. The output goes to one side of the bridged-T frequency determining network. It consist of two resistors and two capacitors. One side goes through a series resistor, then another resistor to the other side. A capacitor goes directly from one side to the other side. Another capacitor connects from the junction of the two resistors to the bottom. The resistors are a set of precision resistors that are selected by the frequency switches. The capacitors are selected by the range switch. This switching is quite complex and will not be described here. Recall that we designated the three connection points of the bridged-T as one side, the other side, and the bottom. As already mentioned the output of the gain block connects to one side. The other side connects to the base of Q1. The bottom of the bridged-T connects to the bottom of a 750 ohm pot which is labeled feedback. The top of the feedback pot goes through a 10 k ohm resistor to the base of Q2. The base of Q2 also goes through a 220 k ohm resistor to plus 43 volts. The wiper of the feedback pot goes through a small incandescent lamp to the output of the gain block. There is a 1.1 k ohm resistor from plus 43 volts to the top of a 750 ohm pot. The bottom of this pot goes through another 1.1 k ohm to ground. This pot is labeled bias. The wiper goes through a 68 microfarad capacitor to ground. The wiper also goes to the bottom of the feedback pot. The output of the gain block also goes through a resistor and then a pot to ground. The pot is labeled symmetry and will be removed from the circuit board as part of the modifications. The wiper of this pot goes to the base of Q6 which was originally part of the schmitt trigger that formed the square wave. Q6 will be converted into a current sink for D1 and D2. The output of the gain block also goes through a 250 microfarad capacitor to the top of the output control, a 5 k ohm pot. The bottom is grounded. The wiper of the output pot goes through a 150 ohm resistor to the step attenuator. It will not be described. The end of the 150 ohm resistor away from the output pot goes through a 620 ohm resistor than another pot to ground. This is the meter cal pot. Its wiper goes to the cathode and anode of D3 and D4 respectively. The other ends of the diodes go through 10 k ohm resistors to ground, one for each diode. A meter, the front panel output meter, connects between the anode of D3 and the cathode of D4. Turning the meter cal pot to zero will take the meter and its diodes out of the circuit. Power supply. The power transformer is equipped with a duo voltage primary, 120/240 volts. The secondary is center-tapped and the center-tap, yellow, is grounded. One end of the secondary, red, goes to the anode of diode D5. The other end of the secondary, red, goes to the anode of D6. The cathodes of D5 and D6 are tied together and go to the positive side of C1, a 300 microfarad capacitor. The negative side is grounded. The positive side of C1 goes through R27, a 47 ohm resistor to the positive side of C2, also a 300 microfarad. The negative side is grounded. The positive side of C2 goes through R28, a 2.4 k ohm resistor to the cathode of a zener diode, D7. The anode is grounded. The cathode of the zener goes to the base of an NPN transistor, Q10. The base of Q10 also goes to the positive side of C3, a 300 microfarad capacitor. The negative side of C3 is grounded. The collector of Q10 goes to the positive side of C2. The emitter of Q10 goes to the positive side of C4, a 50 microfarad capacitor, the negative side is grounded. The emitter of Q10 is the plus 43 volt output. Modifications. The power supply is to be seriously modified. R28, D7, C3, and Q10 are all to be removed. An LM317 voltage regulator circuit will take its place as follows. The positive side of C2 goes to the input terminal of U1, LM317. There is a 0.1 microfarad 100 volt capacitor connected from the input terminal of U1 to ground. The adjust terminal of U1 goes through a selected resistor to ground. The resistor is a 3.9 k ohm 1/2 watt 10% which has been selected to have a resistance of 4.3 k ohms. There is a 10 microfarad capacitor in parallel with the selected resistor with its positive terminal going to the adjust terminal of U1. The output terminal of U1 goes through a 120 ohm resistor to the adjust terminal. The output terminal also goes to the positive side of C4. This completes the power supply modification. See the main text for more information. Oscillator modifications. The symmetry pot for the square-wave generator is removed from the board. Q6 is left in place but Q7 and all resistors and capacitors connecting to Q6 are removed. Resistors may be installed in existing holes in the circuit board. There is a 1 k ohm resistor connecting from the emitter of Q6 to ground. There is a 2.7 k ohm resistor connecting from the base of Q6 to ground. There is a 43 k ohm resistor connected from the base of Q6 to plus 43 volts. The 10 k ohm resistor from the base of Q5 to ground is removed. A piece of hookup wire is used to connect the collector of Q6 to the base of Q5. See main text for more information. End verbal description.