Tech Support Biasing the CA-770



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
 
Procedures

To check and adjust the bias voltage of the EL34 tubes, simply follow the following procedures:
  1. Making sure that the power switch is in the OFF position.


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


  3. 3. Loosen the screws that secure the top cover of the amplifier to the chassis. Remove the top cover to get access to the inside of the 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. Carefully insert the positive test lead into the bias measuring point labeled as T1 on the main PC board.


  7. Carefully insert a long-handled slotted screwdriver into the bias adjustment pot labeled as VR1 on the PC board. Slowly rotate the screwdriver to adjust the bias voltage until it reaches 0.35V.


  8. Repeat steps 6 and 7 to adjust the bias voltage for the three remaining tubes in the same fashion as biasing the first one. Use measuring points labeled as “T2, T3 and T4” for measuring, and bias adjustment pots labeled as “VR2, VR3 and VR4” for adjusting. You will need to go back and forth a few times until all four tubes are properly biased.


  9. Once you have finished biasing all four tubes, wait a few minutes and recheck the settings again.


  10. Turn the power OFF. Detach the negative test lead from the chassis. Put the top cover and the screws back on to the amplifier.


  11. The CA-770 power amplifier is now ready to use.


 


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