TUBES MAINTENANCE
Positions of tubes in the amplifier
MODEL
FUNCTION
V1 12AX7
first preamp tube
V2 12AX7
second preamp tube (only for distorted
channel)
V3 12AX7
third preamp tube
V4 12AX7
phase inverter tube
V5÷V8 6L6WGC / 5881
power tube
V9÷V10 5C3S (5U4G)
rectifier tube
Hints concerning tubes.
Tube replacement and bias adjustment should only be performed by qualified personnel.
Tubes can get very hot and touching them may result in burnts. Therefore the amplifier needs to be
turned off, unplugged and allowed to cool down before maintenance is performed.
Before you change tubes, pay attention to the correct alignment of the pins to the socket.
When the sound quality of the amp starts to decrease over time, a tube replacement might
be in order. One indicator is a loss of high frequencies and dynamic range. There are other signs
that indicate that tubes should be changed: a red outer metal cover, which is normally grey; flashes
inside the tube and other irregular behaviour.
Use only new tubes. Power tubes should all be changed at the same time for a quartet of
5881/6L6WGC tubes. The 5881 are more mechanically reliable version of 6L6. Both of the sets can
be purchased from Laboga.
The amplifier’s design also features a power tube symmetry regulation - see point 9 on page
12. Such regulation should be attempted only after you read the instruction point 9, page 12.
However, you cannot change the Bias value. Various tests helped to choose the best possible bias,
setting, therefore we’ve decided to fix the bias value to avoid changes. This has been done to
improve the amplifier’s reliability.
13
To Next Page
Loading...