CHANGE OF TUBES IN THE AMPLIFIER
Positions of tubes in the amplifier:
MODEL
FUNCTION
V1
12AX7
first preamp tube
V2
12AX7
second preamp tube
V3
÷
V6
EL84
power tubes
Hints concerning tubes.
Leave tube change and bias setting for qualified personnel. Tubes could get heated
intensively. If you touch them, you can get burnt. That is why, before you change tubes, turn
amplifier off, take the plug out and wait for them to cool down.
Before you change tubes, pay attention if their pins are straight because the feet have to be
positioned in a certain way.
The first sign informing that tubes should be changed is worse sound of the amplifier. The
sound gets flat and the dynamics are worse. There are certain signs that imply tubes should be
changed: red outer metal cover, which is normally gray; flashes inside the tube, or other unusual
signs.
Use only new tubes. Power tubes should all be changed at the same time for a quartet of
EL84 tubes. It is a pentode, which is characterized by having a longer life span and is more
mechanically reliable than EL34 for example. A quartet of power tubes, like any other tubes, can be
purchased in a Laboga service.
It is recommended to use V1 and V2 with low noise and/or “low microphonics”. Because the
amplifier has high sensitivity, hums may appear when all the knobs are set “to the right” position
and the amplifier is on the distorted channel.
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