THALES ELECTRON DEVICES TED (ex THOMSON TUBES ELECTRONIQUES TTE) has developed and manufactured a new high power klystron, the TH1801 multibeam klystron (MBK).This tube is planned to equip the TESLA linear collider in Germany.This 10 MW 1.3 GHz MBK operates at a pulse duration of 1.5 ms and a repetition rate of up to 10 Hz, with a efficiency in order of 70%.These performances are not achievable with a single beam klystron, but with a MBK which uses 7 low perveance electron beams.When compared to a conventional klystron, the basic advantages of such a solution are the lower cathode voltage, which allow long pulse operation, and higher achievable efficiency.This MBK is in operation at the TESLA Test Facility, where it was tested at full pulse duration of 1.5 ms. It reached 10 MW at 117 kV and 131 A with an efficiency of 65 %.This paper reports on the tubes and the test results of the TH1801 Multi Beam Klystrons built until now.