Heathkit Model IG-1272
Audio Generator
Date Calibrated: _____/_____/_____
Calibration Procedure
· With the power supply off, the meter pointer should be over the zero reading 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 (analog)
25 MHz Oscilloscope
50 W coax cable (RG-58)
Frequency Counter
High Impedance VTVM
Distortion Analyzer (optional)
* * * * * * *
FRONT PANEL INITIAL SETUP
Refer to PICTORIAL 4-2
Illustration Booklet, page 7
( ) Adjust the LEVEL control counter-clockwise to the OFF position.
( ) Set the X100 MULTIPLIER pushbutton to the ON (in) position.
( ) Set the 10 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Set the 10 ATTENUATOR pushbutton to the OFF (out) position.
( ) Set the 20 ATTENUATOR pushbutton to the OFF (out) position.
( ) Set the 40 ATTENUATOR pushbutton to the OFF (out) position.
( ) Set the EXT LOAD pushbutton in the OFF (out) position.
* * * * * * *
CIRCUIT BOARD INITIAL SETUP
Refer to PICTORIAL 4-3
Illustration Booklet, page 7
( ) Adjust the METER ADJ control [R132] to the center of rotation.
( ) Adjust the DIST ADJ control [R109] to the center of rotation.
( ) Adjust the X1000 ADJ control [R107] to the center of rotation.
( ) Adjust the BIAS ADJ control [R112] to the 10 o’clock position.
( ) Adjust the FREQ ADJ trimmer [C101] to the center of rotation.
(Position the notch as shown in the PICTORIAL.)
* * * * * * *
CALIBRATION
( ) Connect the line cord to the AC power line.
( ) Adjust the LEVEL control clockwise until the click. (Pilot lamp should light.)
( ) Adjust the LEVEL control to maximum clockwise.
( ) Adjust the METER ADJ control [R132] counter-clockwise until the meter indicates full scale on the 10-volt scale.
* * * * * * *
Oscilloscope Setup
( ) Set the oscilloscope’s vertical attenuator for a 40-volt input signal.
· If the oscilloscope will not display a 40-volt signal, use a X10 attenuator probe. DO NOT readjust the Generator’s LEVEL control.
( ) Set the oscilloscope’s horizontal sweep for a 1000 Hz [1 ms] signal.
( ) Connect a coax cable to the oscilloscope’s vertical input.
* * * * * * *
Generator Setup
( ) Set the X1000 MULTIPLIER pushbutton to the ON (in) position.
( ) Set the 10 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Set the EXT LOAD pushbutton in the OFF (out) position.
( ) Adjust the LEVEL control to maximum clockwise.
( ) Connect the same coax cable to the 10V OUT output jack of the generator.
( ) Adjust the DIST ADJ control [R109] until the oscilloscope’s trace is just clipping on both peaks of the waveform.
( ) Adjust the BIAS ADJ control [R112] for symmetrical clipping of the trace.
( ) Adjust the DIST ADJ control [R109] until the clipping just disappears.
( ) Adjust the LEVEL control to the maximum counter-clockwise OFF position.
( ) Disconnect the oscilloscope from the generator.
* * * * * * *
AC VTVM setup
Refer to PICTORIAL 4-3 & 4-5
Illustration Booklet, pages 7 & 8
( ) Set the AC VTVM on the 10-volt scale.
( ) Connect a coax cable, or a set of test leads, to the AC VTVM’s input jacks.
( ) Connect the same coax cable, or set of test leads, to the 10V OUT output jack of the generator.
( ) Set the X100 MULTIPLIER pushbutton to the ON (in) position.
( ) Set the 10 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Adjust the LEVEL control to maximum clockwise.
( ) Adjust the DIST ADJ control [R109] for a 10-volt AC VTVM reading.
( ) Adjust the METER ADJ control [R132] for a 10-volt front panel indication.
( ) Set the X1000 MULTIPLIER pushbutton to the ON (in) position.
( ) Adjust the X1000 ADJ control [R107] until the front panel meter indicates full scale on the 10-volt scale.
( ) Disconnect the AC VTVM from the generator.
* * * * * * *
Oscilloscope setup
( ) Connect the oscilloscope the same as above.
( ) Set the 90 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Adjust the LEVEL control to maximum clockwise.
( ) Observe the oscilloscope’s trace for clipping.
( ) Adjust the BIAS control [R112] for either no clipping or symmetrical clipping.
( ) Adjust the LEVEL control to the maximum counter-clockwise OFF position.
( ) Disconnect the oscilloscope from the generator.
* * * * * * *
HIGH FREQUENCY CALIBRATION
Frequency Counter setup
( ) Connect a coax cable to the frequency counter.
( ) Connect the same coax cable to the 10V OUT output jack of the generator.
( ) Set the X1000 MULTIPLIER pushbutton to the ON (in) position.
( ) Set the 0 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Adjust the LEVEL control to maximum clockwise.
( ) Adjust the FREQ ADJ trimmer [C101] for a Frequency Counter reading of 90 kHz +/- 2 kHz.
* * * * * * *
FUNCTIONAL CHECKS
Variable Frequency Control Check
( ) Set the 0 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Set the X1 MULTIPLIER pushbutton to the ON (in) position.
( ) Perform the three marked steps X1 below.
( ) The readings should be approximately 9 Hz to approximately 110 Hz.
X1 X10 X100 X1000
( ) ( ) ( ) ( )1 Adjust the VARIABLE FREQUENCY control [R3/R4] to maximum counter-clockwise.
( ) ( ) ( ) ( )2 Adjust the VARIABLE FREQUENCY control slowly to maximum clockwise.
( ) ( ) ( ) ( )3 Adjust the LEVEL control to maximum counter-clockwise OFF position.
( ) Set the X10 MULTIPLIER pushbutton to the ON (in) position.
( ) Repeat the three marked steps X10 above.
( ) The readings should be approximately 90 Hz to approximately 1100 Hz.
( ) Set the X100 MULTIPLIER pushbutton to the ON (in) position.
( ) Repeat the three marked steps X100 above.
( ) The readings should be approximately 900 Hz to approximately 11 kHz.
( ) Set the X1000 MULTIPLIER pushbutton to the ON (in) position.
( ) Repeat the three marked steps X1000 above.
( ) The readings should be approximately 9 kHz to approximately 110 kHz.
( ) Disconnect the frequency counter from the generator.
Selector Switch Check
( ) Set the X1000 MULTIPLIER pushbutton to the ON (in) position.
( ) Repeat the two marked steps 1 below for each pushbutton (0 –> 90) of the 0–90 selector switch bank.
0 10 20 30 40 50 60 70 80 90 Set the X pushbutton of the 0–90 selector switch bank to the
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )1 ON (in) position.
0 10 20 30 40 50 60 70 80 90 Observe the meter reading at each switch position, indication
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )1 should stay the same.
( ) Repeat the two marked steps 2 below for each pushbutton (0 –> 9) of the 0–9 selector switch bank.
0 1 2 3 4 5 6 7 8 9 Set the X pushbutton of the 0–9 selector switch bank to the
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )2 ON (in) position.
0 1 2 3 4 5 6 7 8 9 Observe the meter reading at each switch position, indication
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )2 should stay the same.
( ) Repeat the two marked steps 3 below for each pushbutton (0 –> .9) of the 0–0.9 selector switch bank.
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 Set the X pushbutton of the 0–0.9 selector switch bank to the
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )3 ON (in) position.
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 Observe the meter reading at each switch position, indication
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )3 should stay the same.
( ) Adjust the LEVEL control to the maximum counter-clockwise OFF position.
Attenuator Switches and External Load Switch Check
· The accuracy of these measurements will be +/- .2 dB +/- the accuracy of the AC VTVM.
( ) Set the AC VTVM to measure from 10 to 70 dB.
( ) Connect the AC VTVM to the 10V OUT output jack of the generator.
( ) Set the X100 MULTIPLIER pushbutton to the ON (in) position.
( ) Set the 0 pushbutton of the 0–90 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–9 selector switch bank to the ON (in) position.
( ) Set the 0 pushbutton of the 0–0.9 selector switch bank to the ON (in) position.
( ) Set all three ATTENUATOR pushbuttons to the OFF (out) position.
( ) Record the AC VTVM reading. __________
( ) Set the X10 ATTENUATOR pushbutton to the ON (in) position.
(The reading should be 10 dB below original meter indication)
( ) Set the X10 ATTENUATOR pushbutton to the OFF (out) position.
( ) Set the X20 ATTENUATOR pushbutton to the ON (in) position.
(The reading should be 20 dB below original meter indication)
( ) Set both the X10 and X20 ATTENUATOR pushbuttons to the ON (in) position.
(The reading should be 30 dB below original meter indication)
( ) Set both the X10 and X20 ATTENUATOR pushbuttons to the OFF (out) position.
( ) Set the X40 ATTENUATOR pushbutton to the ON (in) position.
(The reading should be 40 dB below original meter reading)
( ) Set both the X10 and X40 ATTENUATOR pushbuttons to the ON (in) position.
(The reading should be 50 dB below original meter indication)
( ) Set the X10 ATTENUATOR pushbutton to the OFF (out) position.
( ) Set both the X20 and X40 ATTENUATOR pushbuttons to the ON (in) position.
(The reading should be 60 dB below original meter indication)
( ) Set all the X10, X20, and X40 ATTENUATOR pushbuttons to the ON (in) position.
(The reading should be 70 dB below original meter indication)
( ) Set the AC VTVM on the 10-volt scale.
( ) Set all three ATTENUATOR pushbuttons to the OFF (out) position.
( ) Set the EXT LOAD pushbutton to the ON (in) position.
(The AC VTVM reading should increase slightly.)
( ) Set the EXT LOAD pushbutton to the OFF (out) position.
(The original AC VTVM indication should return.)
( ) Disconnect the AC VTVM.
( ) Connect a high impedance (12 kW or higher) voltmeter [VTVM] to the SYNC output [rear of unit].
( ) The meter reading should be at least 1 volt rms.
♦ After the unit has been operated for at least 48 hours, readjust both the DIST ADJ [R109] and the METER ADJ [R132] controls for a 10-volt output.
( ) Disconnect all test leads and cables from the unit.
( ) Set the POWER switch to the OFF position.
( ) Disconnect the line cord from the AC power lines.
( ) Calibration procedure is complete.