Patent ID: 8705772
Filing Date: 2014-04-22
Classification: H03F

Abstract:
1. A valve power amplifier stage for an audio amplifier, the valve power amplifier stage comprising at least one thermionic valve and polarization means for polarizing the anode, the cathode and the control grid of said at least one thermionic valve so as to determine the maximum output power deliverable by the thermionic valve; the valve power amplifier stage being characterized in that said polarization means comprise: electronic adjusting means for adjusting the feed voltage of the anode and the polarization voltage of the control grid in such a way as to adjust the maximum output power of said at least one thermionic valve; and selecting means coupled with said adjusting means for allowing a user to control said adjusting means so as to select the desired maximum output power among a plurality of predetermined output power values, wherein said adjusting means comprise: first voltage supplying means for supplying voltage to said anode; second voltage supplying means for polarizing said control grid; processing and control means for receiving a selection signal from said selecting means and for generating, as a function of the 19 selection signal, a first control signal, which is representative of an anode voltage value and is suited to control said first voltage supplying means in such a way that said anode voltage value is applied to the anode, and at least one second control signal, which is representative of a grid voltage value and is suited to control said second voltage supplying means in such a way that said grid voltage value is applied to the control grid, and wherein said processing and control means comprise memory means for memorizing at least one data table associated to said at least one thermionic valve, the data table comprising a plurality of anode voltage values and a corresponding plurality of grid voltage values, each pair of anode voltage and grid voltage values being associated to a respective one of said predetermined output power values; said processing and control means being configured to address the data table as a function of said selection signal so as to select one of said pairs of voltage values and to generate said first control signal as a function of the selected anode voltage value and said at least one second control signal as a function of the selected grid voltage value.