andrews Para-Dyne 20, Руководство по эксплуатации

Страница: 10 / 12

10
FOR TECHNICAL TYPES
We have provided this information for those who have a technical interest,
proper equipment and a DYI attitude. CAUTION! GUITAR AMPLIFIERS
CONTAIN LETHAL VOLTAGES. If you have any doubt about your ability to
safely perform this procedure, refer the job to a qualified technician!
Bias Adjustment Procedure:
Precautions:
•
Lethal voltages are present inside the chassis and at the tube pins. Do not
open the chassis or insert any objects into any openings other than where
directed by these instructions. The entire procedure can be accomplished
without opening the amp.
•
Vacuum tubes get very hot. Always allow the tubes to cool completely before
touching them.
•
When replacing output tubes, use only the very highest quality tubes or the
amplifier may be damaged. For more details, see the section below regarding
tube replacement.
1) Unplug the amplifier and allow the tubes to cool. The output tubes are the two tall
tubes on the left side of the amp when viewed from behind.
2) Unsnap or spread open the retaining clips that hold the output tubes in place and
remove the tubes. Install a new matched pair of the same type of output tubes that
came installed in your amp. i.e. EL34, 6V6 or 6L6
3) Utilizing a digital multi-meter, set for DC Volts or millivolts measurement and select
a range that will show 0-100 millivolts. Insert the black meter lead into the black
test point terminal and insert the red meter lead into the red test point terminal.
4)
Insert a small flat blade screwdriver into the adjustment control hole and gently
turn the control to its mid position. The adjustment control is located on the
underside of the chassis near the bias test points.
5) Plug in the AC cord and turn on the amplifier’s main power switch. After waiting at
least one minute, turn on the standby switch. The meter should display a few
millivolts (mV).
6) While taking care not to touch any hot tubes, insert the screwdriver into the
adjustment control slot and very slowly turn the adjustment until the meter reads
65mV for EL34 amps, 75mV for 6L6 amps, 44mV for 6V6 amps and 40mV for
EL84 amps. The test point shows the combined reading for both output tubes.
7)
It’s a good idea to re-check the bias periodically (every 500 hours of use) as the
idle current can drift over time as the tubes age.