An S-band klystron of 50 MW power is being developed at the Budker Institute of Nuclear Physics. At the moment, all the necessary calculations have been made and cathode assembly, bunching cavities, the collector, the solenoid, and the cooling system have been completed. The klystron has been tested in a diode mode without bunching cavities, which were brazed separately. Cavities have been measured and tuned at the required frequencies and installed on the prototype of the klystron. Currently, a fully finished prototype is being tested in order to obtain RF power.