Tech Support Biasing the CA-303

Disclaimer of Liability

Under no circumstances does Canary Audio assume liability or responsibility for injury or damages sustained in biasing this equipment or for damages to any other equipment connected to it.

Even though we provided the procedures, we suggest that these adjustments to be performed only by an authorized Canary Audio dealer or repair center as an incorrect bias setting can cause damages to the tube and to the amplifier.
Tools Required

Digital multimeter
Long-handled slotted screwdriver

To check and adjust the bias voltage of the 300B tubes, simply follow the following procedures:
  1. Making sure that the power switch is in the OFF position.

  2. Install all the tubes to the corresponding sockets using gentle rocking motion.

  3. Connect your speaker leads, input cable and power cord to the amplifier.

  4. Carefully turn the amplifier upside down or turn it up vertically. Unscrew the bottom metal plate to get access to the inside of the amplifier.

  5. Turn ON the amplifier.

  6. 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.

  7. Carefully attach the positive test lead to the soldering point marked as C1 on the main PC board for measuring.

  8. Carefully insert a long-handled slotted screwdriver into the bias adjustment pot marked as VR1 on the PC board. Slowly rotate the screwdriver to adjust the bias voltage until it reaches 0.55V.

  9. Repeat steps 7 and 8 to adjust the bias voltage for the remaining 300B tubes in the same fashion as biasing the first one. Use soldering points marked as C2 for measuring, and bias adjustment pots marked as VR2 for adjusting. You will need to go back and forth a few times until both 300B tubes are properly biased.

  10. Once you have finished biasing the two 300B tubes, wait a few minutes and recheck the settings again.

  11. Turn the power OFF. Detach the negative test lead from the chassis. Put the bottom metal plate and the screws back on. Carefully place the amplifier back to a horizontal position.

  12. Repeat these procedures to adjust the bias voltage for the 300B tubes on the other channel of the amplifier.

  13. The CA-303 mono blocks power amplifier is now ready to use.


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