288 Monaural Amplifier Rev 1.2
10
We recommend the following tube replacement schedule:
•
Under normal bias conditions, power tubes typically last 2 years depending on hours of use
and average listening volume. Speakers demanding maximum power may push the tube
lifespan to less than 2 years. With very efficient speakers, which require little power for
acceptable listening levels, tubes can last much longer than 2 years.
•
Preamp tubes will last longer than power tubes, assuming no premature failures. We
recommend changing preamp tubes every other time the power tubes are changed unless
the utmost performance is demanded or they have gone bad.
•
The tube rectifiers only need to be replaced when they fail. There is no need for regular
change unless reliability is a concern or the amplifier has seen a lot of vibration from
transportation. Moving the amps when they are on or hot can damage the rectifier and other
tubes.
Always re-bias your amplifier after changing the power tubes!
The bias of the amplifier should be checked immediately after replacing the KT88 Power tubes
V3 and V4.
A matched pair of KT88 output tubes should be used for V3 and V4 positions. This ensures a
balanced output and low distortion. Matching output tubes between separate amplifier channels is
not critical, but recommended.
Preamp tube V2 contains two sections in a single glass envelope. These sections should be tightly
matched for balance drive to the output tubes.
All tubes from Bandwidth Audio are matched in this fashion.
