Published February 25, 2010
The ADL600 uses a total of three tubes on each channel:  6922 and  12AT7A.
The tube in the first position closest to the rear panel is a 12AT7A. The tubes in the two positions directly behind the faceplate are both EH6922 triodes.
Replacement tubes can be purchased from a variety of vendors.
Please contact PreSonus Technical Support by creating a Support Ticket at My.PreSonus.com for further assistance.