Jadis DA88 Signature Owner's Manual page 9

First of all, remove the tube cage which protects the tubes sockets (be
sure the mains connector is unplugged).
Attention: For mounting the tubes, do not force them, this may
damage the sockets. Be careful at dressing power tubes (A, B, C and D)
because they have stop pins on the central parts of the mounting base.
Mount first the drivers tubes ( 1, 2, 3, 4 and 5) then mount the
power tubes. The tubes placement is shown at the top of this page.
Replace the tube cage and never remove it when the amplifier is
connected to the mains voltage, whether it is running or not.
Tubes position