Heathkit model EUW-27
Sine-Square Generator
Date Calibrated: _____/_____/_____
Calibration Procedure
Ancillary Equipment Needed
AC VTVM (20 Hz – 1 MHz)
VTVM
Audio Harmonic Distortion Meter
15 MHz Oscilloscope
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NOTES
· Remove all loads from both sets of terminals.
· For adjustments inside the shielded area, a non-metallic alignment tool is preferable, but a small screwdriver can be made to work if the blade is insulated with tape, although it may cause a loss in accuracy.
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Initial Front Panel Adjustments
( ) Disconnect the line cord from the AC line voltage.
( ) Remove the top cabinet.
( ) Set the SQUARE WAVE AMPLITUDE control to the AC OFF position.
( ) Set the SQUARE WAVE RANGE switch to the 1V position.
( ) Set the FREQUENCY MULTIPLIER switch to the 1 position.
( ) Set the SINE WAVE AMPLITUDE control to maximum counter-clockwise.
( ) Set the SINE WAVE RANGE switch to the .01V position.
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Initial Internal Adjustments
[refer to Figure 2 – front looking rear]
( ) Adjust the SQUARE WAVE WAVEFORM trimmer [left chassis – center edge] to the center of rotation.
( ) Adjust the SQUARE WAVE SYMMETRY control [left chassis – center] to the center of rotation.
( ) Adjust the 1 MHz coil to the center of its range. [right chassis – center] until a 1/2” of the adjustment screw is visible
( ) Adjust the FEEDBACK control [right chassis – right rear] to the center of rotation.
( ) Adjust the DISTORTION control [right chassis – center rear] to the center of rotation.
( ) Adjust the FREQUENCY trimmer [shield top – front] to the center of rotation.
( ) Adjust the FLATNESS trimmer [shield top – rear] to the center of rotation.
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Dial Adjustment
( ) Set the SQUARE WAVE AMPLITUDE control until the switch clicks to the ON position.
(Allow the instrument to warm up for 15 minutes.)
( ) Adjust the FREQUENCY SELECTOR control to the maximum counter-clockwise.
( ) The FREQUENCY DIAL pointer should be below the 20 mark on the outer scale.
( ) If the FREQUENCY DIAL pointer is not on the marker, loosen the collar set screw. [refer to Figure 3]
( ) Rotate the FREQUENCY DIAL pointer without moving the shaft, until the pointer is on the marker.
( ) Carefully retighten the set screw.
FREQUENCY ADJUSTMENTS
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Using an Oscilloscope
Lissajous Pattern
( ) Measure an accurate 60 Hz reference signal source (filament winding of a power transformer) with an AC VTVM.
( ) Set the oscilloscope’s horizontal and vertical input attenuators to match the 60 Hz reference signal voltage.
( ) Connect the same accurate 60 Hz reference signal above to the oscilloscope’s horizontal input.
( ) Connect the AC VTVM to the Sine Wave output terminals of the generator.
( ) Adjust the SINE WAVE AMPLITUDE control until the Generator output voltage matches the 60 Hz reference voltage as measured using the AC VTVM.
( ) Disconnect the AC VTVM from the generator.
( ) Connect the generator’s output to the oscilloscope’s vertical input.
( ) Adjust the FREQUENCY SELECTOR control until the Lissajous pattern ratio is 1:1 (a circle or a line).
NOTE: With the output frequency set at 120 Hz and 180 Hz, the stable Lissajous pattern will be 2:1 and 3:1 respectively.
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Using an AC VTVM
Zero Beat
( ) Connect the ground lead of the AC VTVM to an accurate 60 Hz reference signal source (filament winding of a power transformer).
( ) Connect the hot lead of the AC VTVM to the positive Square Wave binding post.
NOTE: The square wave signal gives a much better indication of the zero beat.
( ) Connect the other 60 Hz reference signal source lead to the negative Square Wave binding post.
NOTE: This is only necessary if using an external reference source, and not the unit’s filament voltage.
( ) Adjust the AC VTVM attenuation to where there is a reading on the upper half of the meter scale.
( ) Slowly tune the FREQUENCY SELECTOR control through the region around the 60 mark on the outer scale.
The pointer will go through a period of oscillation where the zero beat becomes quite noticeable. Tune very slowly and carefully through this area. Notice that the oscillations start with the meter pointer moving quickly. Gradually it moves more slowly and with larger swings until it reaches a maximum. By tuning carefully, a “zero beat” point can be obtained. Past that point the pointer begins to move again.
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60 Hz Adjustment
( ) ( )1 Adjust the FREQUENCY SELECTOR control to obtain a “zero beat”.
( ) ( )2 Carefully loosen the setscrew on the insulated pointer extension.
( ) ( )3 Adjust the FREQUENCY SELECTOR control pointer to the 60 mark on the outer scale. (60 Hz)
( ) ( )4 Retighten the setscrew on the insulated pointer extension.
( ) Repeat the above four steps until no further dial pointer adjustment is required.
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180 Hz Adjustment
( ) Adjust the FREQUENCY SELECTOR control pointer to the 180 mark on the outer scale. (180 Hz)
( ) Adjust the FREQUENCY ADJUST trimmer [top shield – left front] until a zero beat indication is observed on the AC VTVM’s meter. [refer to Figure 2]
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( ) ( )1 Recheck the 60 Hz FREQUENCY SELECTOR dial pointer adjusted position again.
( ) ( )2 Re-adjust the 60 Hz “zero beat” point if necessary.
( ) ( )3 Recheck the 180 Hz FREQUENCY SELECTOR dial pointer adjusted position again.
( ) ( )4 Re-adjust the 180 Hz “zero beat” point if necessary.
( ) Repeat the above four steps until no further dial pointer adjustment is required.
( ) Disconnect the AC VTVM test lead from the 60 Hz reference signal source.
( ) Disconnect all test leads from the generator’s output terminals.
OUTPUT VOLTAGE ADJUSTMENTS
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10-volt Output Level Adjustment
( ) Set the FREQUENCY MULTIPLIER to the 10 position.
( ) Connect the AC VTVM test leads across the Sine Wave output terminals. [refer to Figure 2]
( ) Adjust the FREQUENCY SELECTOR control to the full counterclockwise position.
( ) Adjust the FEEDBACK control [right chassis – rear] to the full counterclockwise position.
( ) Adjust the FEEDBACK control until the AC Voltmeter indicates 10 VAC.
( ) Adjust the FREQUENCY SELECTOR control to the 200 mark on the outer scale. (2 kHz)
( ) Adjust the FLATNESS ADJUST trimmer [top shield – left rear] until the AC Voltmeter indicates 10 VAC.
( ) Set the FREQUENCY MULTIPLIER switch to the 10K position.
( ) Adjust the FREQUENCY SELECTOR control to the 100 mark on the inner scale. (1 MHz)
( ) Adjust the 1 MHz ADJUST coil [right center of chassis] until the AC Voltmeter indicates 10 VAC.
SINE WAVE ADJUSTMENTS
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Ohmmeter Method
[refer to Figure 4A]
NOTE: This method gives the best performance based upon average tube characteristics.
( ) Set the SQUARE WAVE AMPLITUDE control to the AC OFF position.
( ) Remove the bottom chassis plate.
( ) Remove tube V1 (6CB6) from its socket. [right chassis – center rear]
( ) Set the VTVM selector switch to the Ohms position.
( ) Set the VTVM attenuator switch to the RX10 position.
( ) Connect the VTVM’s probes to the two outside lugs of the DISTORTION control. [right chassis – center rear]
( ) Adjust the DISTORTION control for an indication of 130 W.
( ) Disconnect the two VTVM probes from the DISTORTION control lugs.
( ) Insert tube V1 (6CB6) back into its socket.
( ) Replace the bottom chassis plate.
( ) Set the SQUARE WAVE AMPLITUDE control to the ON position.
(Allow the instrument to warm up for 15 minutes.)
( ) Skip down to the SQUARE WAVE ADJUSTMENT section.
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Audio Distortion Meter Method
[refer to Figure 4B]
NOTE: This method gives the best possible bias voltage for the V1 tube installed in the generator.
( ) Connect the Harmonic Distortion Meter to the Sine Wave output terminals.
( ) Connect the AC VTVM to the Sine Wave output terminals.
( ) Set the FREQUENCY MULTIPLIER switch to the 1 position.
( ) Set the SINE WAVE RANGE switch to the 10V position.
( ) Adjust the FREQUENCY SELECTOR control pointer to the 150 mark on the outer scale. (150 Hz)
( ) Adjust the SINE WAVE AMPLITUDE control until the AC VTVM indicates 10 VAC.
( ) Adjust the Harmonic Distortion Meter to indicate the percent of signal distortion.
( ) ( )1 Adjust the DISTORTION control [right chassis – center rear] in either direction until a decrease in the amount of distortion is indicated on the Harmonic Distortion Meter.
( ) ( )2 Adjust the FEEDBACK control [right rear of chassis] until the AC VTVM indicates 10 VAC.
( ) Repeat the above two steps until the minimum distortion is indicated on the Harmonic Distortion Meter.
( ) Disconnect all external test leads from the Sine Wave output terminals.
SQUARE WAVE ADJUSTMENTS
[refer to Figures 2 and 5]
( ) Set the oscilloscope’s input to 2 volts/cm.
( ) Set the oscilloscope’s sweep rate to 1 ms/cm.
( ) Connect the Oscilloscope to the Square Wave output terminals.
( ) Set the SQUARE WAVE RANGE switch to the 10V position.
( ) Set the FREQUENCY MULTIPLIER switch to the 10 position.
( ) Adjust the FREQUENCY SELECTOR control pointer to the 200 mark on the outer scale. (2 kHz)
( ) Adjust the SQUARE WAVE AMPLITUDE control for a 10 VAC P-P trace.
( ) Adjust the SQUARE SYMMETRY control [left chassis – next to shield] until both positive and negative halves of the square wave are of equal duration.
( ) Set the FREQUENCY MULTIPLIER switch to the 100 position. (20 kHz)
( ) Adjust the SQUARE WAVE WAVEFORM control [left chassis – outside center] for the sharpest rise time and corners of the square wave.
( ) Disconnect all external components from all the front terminals.
( ) Disconnect the line cord from the AC line source.
( ) Calibration procedure is complete.