5.1 DC Bias Voltage Tuning
Since each tube might derivate a bit in parameters, especially from different
series, it needs to re-tune the DC bias voltages to guarantee the machine is
working in the best point and performing the best sound quality.
There are two blue precise adjustable potentiometers (RP1, RP2) for tuning
the DC bias voltage of each channel. The DC bias has been tuned tin factory.
But after run-in for a period of time or changed another tube, it would be
deviated that the fine-tuning is needed.
Before you tune these, you need a screwdriver (take off the case), a small
screwdriver (Turn the screw of the potentiometer) and a (digital) multi-meter to
detect the DC bias voltage:
1.
Remove the crystal block to access the tube. Slowly shake the vacuum
tube back and forth to remove the vacuum tube. Plug in your preferred
vacuum tube and select the voltage at the jumper (P2)
2.
Use screwdriver to take out the 4 screws at the bottom of the unit and
remove the base plate.
3.
Power ON the machine with no audio signal input.
4.
Wait at least 5 minutes for the machine to run in.
5.
Use the multi-meter to detect the DC voltage between the test point (L),
next to RP1, in the PCB & the GND (e.g. the ring of the power switch or
the outer ring of the RCA sockets) of the LEFT channel.
6. Turn the screw on the top of the RP1 potentiometer by a small
screwdriver clockwise or anticlockwise until the voltage as close as to
+6~+8V.
7.
Then repeat step 5 and 6 for the RIGHT channel by changing the test
point to (R), next to RP2, and turning the screw on the top of the RP2
potentiometer.
8.
Power OFF the amplifier.
9.
Cover back the base plate and tighten the screws.
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