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7. TUBES
7.3. TUBE SERVICE LIFE
Thanks to the protection circuits and soft start electronics, the output tubes used in your
amplifier should achieve an average service life of 5 years.
The driver tubes can last for 10 years or more.
Because the tubes have different service lives, you will never have to renew the entire tube
complement at the same time.
Please note that some tubes need a long time (up to 300 hours) to achieve their optimum
sound quality.
7.4. Replacing tubes
Driver tubes
Replacement driver tubes require no adjustment.
Output tubes:
General procedure:
1. Switch the amplifier off and allow it to cool down for 10 minutes. Remove the old
tubes and fit the new ones.
2. Before you switch the amplifier back on, turn all bias adjustment controls
counterclockwise (this reduces the anode current substantially). You will
hear a click when the controls reach the minimum setting. These con-
trols are three-turn potentiometers, i.e. it takes three revolutions to go
from the maximum to the minimum setting.
3. Switch the amplifier on. After the ‘Wait’ period, all 4 minus-LEDs should illuminate yel-
low. If at this stage any of the LEDs are green or red, this indicates a faulty tube that
must be replaced.
3.1. New, untested output tubes should be burned in with a low anode current. To do this,
leave the amplifier on for 2 hours. Then adjust all the tubes.
3.2. Original Octave tubes
There is no need to burn in original Octave replacement tubes. After re-
placement, leave the power on for 10 minutes to allow the amplifier to
warm up. Then, adjust the bias.
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