INTERNAL ADJUSTMENTS
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IC
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1)
You will have to start out by setting front panel controls to these settings. BYPASS mode, SEP
(LINK OFF), REDUCTION controls counter clockwise (MIN), GAIN to 1:00 or unity, S.C. at
“Flat”. The top will need to be open. There are two screws on the top that hold the top perforated-
panel to the back. Remove these and the perforated top will slide back. Be careful! THERE ARE
HIGH VOLTAGES INSIDE THE LIMITER. DO NOT HOLD THE METAL PART OF THE
SCREWDRIVER. DO NOT PROBE AROUND WITH THE SCREWDRIVER OR FINGERS.
The unit should be on for about 15 minutes to allow for “warming up”.
2 & 3) This adjusts the tube amplifier gain in all modes. 1 KHz sine at 1.23 volts RMS (+4 dBm, 0 VU)
to both inputs. BYPASS mode. Adjust 2 & 3 for unity gain at outputs.
4 & 5) This adjusts VU meter calibration for OUTPUT. Same input, Meter switches to OUTPUT. Adjust for
0 VU on the Meters.
6 & 7) This adjusts the meter zero for Reduction mode. Meter switches to REDUCTION. Adjust for 0 VU
on the Meters.
8 & 9) This adjusts the meter in Reduction mode to reflect the actual gain reduction accurately. You will
probably need to increase the oscillator 10 dB to get Limiting. Switch from BYPASS to IN. Me-
ter switches to OUTPUT. Adjust GAIN controls to get 0 VU on the METERS again, then adjust
REDUCTION controls to reduce the signal to -4dB. Switch METERS to REDUCTION. Adjust 8
& 9 to get -4 dB on the METERS.
10)
This adjusts the gain of the right side chain and adjusts the side chain balance in Link. Switch
the LINK ON. There should be 1 to 2 dB change in the Meters. Adjust 10 so that the meter
is the same for both sides. You may have to re-adjust 8 and 9. Check that both in LINK and
SEPARATE that both channels show the same reduction.
This is a final check to verify that all adjustments are OK and the unit is ready for use. Confirm that 0
VU on the meters is +4 dBm with an external VU meter or VOM that reads between 1.22 and
1.23 volts AC and that gain reduction reads the same on OUTPUT and REDUCTION and that
LINK or UN-LINK does not reduce the gain unevenly on the two sides. Remove the power and
slide the top in all the way where it will fit into a groove in the front panel and put those two top
screws back in. Done !
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6414
6414
12AU7
12AU7
10
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