Heathkit Model IG-18

Sine-Square Wave Audio Generator

Calibration Procedure

· With the power supply off, the meter pointer should be over the zero indication on the meter face.  If it is not, turn the mechanical zero-adjust screw at the bottom of the meter until the pointer is properly aligned.

· Disconnect all external cables, components, and wires from the output terminals.

Ancillary Equipment Needed

AC VTVM

Oscilloscope

* * * * * * *

FRONT PANEL INITIAL ADJUSTMENTS

Refer to Figure 19

Construction Manual page 36

(    )         Disconnect the line cord from the AC power lines.

(    )         Set the POWER switch to the OFF position.

(    )         Set the MULTIPLIER switch to the X100 position.

(    )         Set the TENS FREQUENCY switch to the 10 position.

(    )         Set the UNITS FREQUENCY switch to the 0 position.

(    )         Adjust the FREQUENCY control to the maximum counter-clockwise.

· The word FINE on the front panel refers to the small center knob on each AMPLITUDE control.

· The word COURSE on the front panel refers to the large outer knob on each AMPLITUDE control.

(    )         Set the SINE WAVE AMPITUDE (course) switch to the 10 volts position.

(    )         Adjust the SINE WAVE AMPLITUDE (fine) control to maximum clockwise.

(    )         Set the SQUARE WAVE AMPITUDE (course) switch to the 10 volts position.

(    )         Adjust the SQUARE WAVE AMPLITUDE (fine) control to maximum clockwise.

(    )         Set the 600 W LOAD switch [below meter] to the EXT position.

* * * * * * *

WAVE GENERATOR CIRCUIT BOARD INITIAL ADJUSTMENTS

Refer to Figure 1

Construction Manual page 36

(    )         Adjust the BIAS control to the center of rotation.

(    )         Adjust the FEEDBACK control to the center of rotation.

(    )         Adjust the METER CAL control to the center of rotation.

(    )         Adjust the SYMMETRY control to the center of rotation.

* * * * * * *

SINE WAVE SYMMETRY ADJUSTMENTS

Refer to Figure 2

Construction Manual page 43

(    )         Connect the line cord from the AC power lines.

(    )         Set the POWER switch to the ON position.

(    )         Adjust the FEEDBACK control until the panel meter indicates between 6 and 8, on the 0 – 10 scale.

(    )         Set the AC VTVM to read 10 volts.

(    )         Connect the AC VTVM to the sine wave output binding posts.

(    )         Adjust the METER CAL control until the panel meter indicates the same reading as the AC VTVM.

(    )         Disconnect the AC VTVM from the binding posts.

(    )         Setup the Oscilloscope to display a 1000 Hz [1 millisecond] waveform with an amplitude of 10 volts.

(    )         Connect the Oscilloscope to the sine wave output binding posts.

(    )         Adjust the FEEDBACK control to maximum clockwise.

(    )         Either the positive or negative half of the peak sine wave trace should be clipped as shown in part A or B of Figure 2.

(    )         Adjust the BIAS control until both halves of the sine wave trace are clipped equally as shown in part C of Figure 2.

(    )         Adjust the FEEDBACK control until the panel meter indicates 10 volts.

(    )         Disconnect the Oscilloscope from the sine wave output binding posts.

(    )         Set the TENS FREQUENCY switch to the 10 position.

· In the following 4 steps *, if no change can be detected in the panel meter indication, no adjustment of the FEEDBACK control is necessary.

(    )*       Increment the TENS FREQUENCY switch from the 10 position through the 100 position.

               (Note the meter voltage indication at each position.)

(    )*       Set the TENS FREQUENCY switch at the lowest meter indication position.

(    )*       Increment the MULTIPLIER switch from the X1 position through the X1000 position.

               (Note the meter voltage indication at each position.)

(    )*       Set the MULTIPLIER switch at the lowest meter indication position.

(    )         Adjust the FEEDBACK control until the panel meter indicates 10 volts.

* * * * * * *

SQUARE WAVE SYMMETRY ADJUSTMENTS

Refer to Figure 3

Construction Manual page 43

(    )         Set the TENS FREQUENCY switch to the 10 position.

(    )         Set the MULTIPLIER switch to the X100 position.

(    )         Set the Oscilloscope input to AC.

(    )         Connect the Oscilloscope to the square wave output binding posts.

(    )         Adjust the SYMMETRY control until both halves of the square wave trace are equal as shown in part C of Figure 3.

(    )         Disconnect the Oscilloscope from the square wave output binding posts.

(    )         Disconnect all external cables from the output terminals.

(    )         Set the POWER switch to the OFF position.

(    )         Disconnect the line cord from the AC power lines.

(    )         Calibration procedure is complete.