TELEFUNKEN vacuum tubes have been the benchmark of excellence in all audio applications, both production and reproduction, for many decades. This rich history continues with the introduction of new production Black Diamond Series tubes from TELEFUNKEN Elektroakustik,as well as tubes from Telefunken's private new old stock collection, now being made available, in limited quantities, direct from the TELEFUNKEN Lab. TELEFUNKEN Elektroakustik will not be held responsible (financially or otherwise) for equipment that is damaged from the use of tubes purchased from us. Each tube has been fully tested to ensure reliability and is guaranteed to perform as described. It is the responsibility of the customer to consult with the equipment manufacturer (or qualified technician) for the selection of proper tubes and proper installation and biasing procedures.