PreSonus TubePRE - Manual (Page 13)

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how hard the tube is driven when in use. Signs of wear may be
exhibited by poor performance or by the tube becoming “microphonic”.
Periodic replacement of the vacuum tube is recommended. The time
between the suggested replacements varies greatly with use. If you
notice deterioration in sound quality then it’s time to change the tube.
Replacing the tube in the TubePRE
1. Unplug the unit. Proceed with caution, as the tube could be hot.
Remove the two screws from the top and the two screws from the
bottom of the unit. Also remove the two screws that surround each of
the XLR plugs.
2. Carefully remove the plastic hex nut that is on the unbalanced
output and the instrument input.
3. Remove the left side panel.
4. Remove the black chassis.
5. Place your thumb on the backside of the card that holds the tube
and carefully unplug the tube.
6. Align the pins of the new tube and place it in the socket with your
thumb again on the back of the tube socket card. Make sure that the
tube is completely seated in the receptacle.
7. Replace the chassis, side, hex nuts and screws.
3.6 Application Guide
Direct Box
The 1/4” and XLR outputs can always be used simultaneously. The
instrument should be plugged into the 1/4” instrument input. The 1/4”
output can be connected to an amplifier on stage and the XLR output
could be connected to the PA system or monitoring mixer.