Service Adjustments - Manley Stereo Variable Mu Owner's Manual

These are factory presets. These should only be altered after a re-tube.
A METER CAL - GR ACCURACY
1. Supply a line level input signal (1K TONE OK)
2. Adjust front controls for NO LIMITING
3. Back down the reduction control to achieve 6dB of actual limiting as observed on an external
calibrated audio frequency test meter.
4. Adjust each channel's trimpot located on the extreme back edges on horizontal PCB to calibrate.
B METER - Adjusts meter "ZERO". Needs to be well warmed up.
1. Set in Limit Mode. No Signal
2. Adjust front panel METER ADJUST so that meter reads ZERO gain reduction.
C 3. COMPRESS TRIM - Also adjusts meter ZERO but in compress mode.
4. Locate the internal trimmers directly next to the meters.
5. Switch to COMPRESS and adjust trimmer for ZERO on the meter.
The above adjustments interact - The order of adjustments needs to be followed. It is worth doing
these steps again to fine tune the trims.
D. To adjust internal balance and lowest distortion:
NOTE: This unit has been factory set for the lowest THD and optimum AC balance. It is recommended
that this control be reset only after changing 5670 tubes.
1. Adjusting this control adjusts the current draw of the 5670 cathodes.
2. Set a multimeter to read DC volts.
3. Connect a good DC voltmeter to the two test points below the GR meter.
4. Adjust the small trim pot located on the front panel and marked "ADJUST" until the METER nulls to zero.
E 5. This procedure is best done by ear with loud drum tracks. Set Attack and Recovery for fastest settings and at
least 6 dB of Limiting. Start the trimmer at center and while listening carefully to the output adjust the trim for
minimum "thumping". We select 5670's to minimise this. Trim procedure "D" also affects "thumping". The best
procedure involves all of these. We push the limit on the attack time for this circuit and symetry is critical.
TROUBLESHOOTING NOTE: Occasionally we have had units sent to us to service that had no problem. The symptom
was clipping only when the unit was in the processing chain. Remove the unit and distortion gone. However in
the shop - no problem. The cause was a combination of the somewhat low input impedance of the Limiter/
Compressor and the somewhat "wimpy" line driver of the preceding device. The solution - change the order of
processing so that a more professional device fed the Limiter / Compressor. The input impedance is over
1Kohm and most devices are supposed to drive 600 ohms (which is twice as hard) but in this era of ICs and
semi-pro gear claiming to be pro well.......
A
METER CAL
SERVICE
D B
6386
12AL5
C
TUBES
E
12AX7A
12BH7
ADJUSTMENTS
6386
12AX7A
15
B
D
12AL5
C
TUBES
E
12BH7
A
METER CAL