Any regulated (DC 0...300V, 100mA) laboratory power supply will work. Good regulated 300V power supplies are produced by Delta Elektronika, postbus 27, 4300 AA Zierikzee, The Netherlands, tel. (0)111-413656, fax (0)11-416919. EMCO high-voltage DC to DC convertors F03 (F02 for lower voltage) can be used for portable applications. One module is needed for a 19-ch system, two modules will power a 37-ch system. In general, you will need one module per 20 channels.