Tube Biasing - CANARY AUDIO CA-339 Owner's Manual

TUBE BIASING

Bias voltage applied to the grids of the power tubes in the output stage should be
checked from time to time to keep these tubes operation at the optimum
operating point. A properly biased power tube will have a longer life.
To check and adjust the bias voltage of the 300B tubes, simply follow the
following procedures.
Tools Required:
Digital Multimeter
Long-handled slotted screwdriver
Procedures:
1. Making sure that the power switch is in the OFF position.
2. Install all the tubes to the corresponding sockets using a gentle rocking
motion. (See "Installing the Vacuum Tubes" section for detail information on
installing the tubes.)
3. Connect your speaker leads, input cable and power cord to each amplifier.
4. Turn ON the amplifier.
5. Turn on the multimeter. Select the section for measuring up to 20V DC.
Attach and secure the negative test lead to the chassis or to the binding post.
6. Insert the positive test lead into the bias test point marked as "300B - V1".
7. Carefully insert a long-handled slotted screwdriver into the bias adjustment
pot marked as "V1". Slowly rotate the screwdriver to adjust the bias voltage
until it reaches 0.55V.
8. Repeat steps 6 and 7 to adjust the bias voltage for the three remaining 300B
tubs in the same fashion as biasing 300B - V1. Using bias test points marked
as "300B - V2, 300B - V3 and 300B - V4" for measuring, and bias adjustment
pot marked as "V2, V3 and V4" for adjusting. You will need to go back and
forth a few times until all four 300B tubes are properly biased.
9. Once you have finished biasing all four 300B tubes, wait a few minutes and
recheck the settings again.
10. Repeat these procedures to adjust the bias voltage for the 300B tubes on the
other channel of the amplifier.
11. The CA-339 mono blocks power amplifier is now ready to use.