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12-27-2025, 01:16 PM
Hi Guys
Before Marshall introduced EPA, they tried a different approach called VPR, Virtual Power Reduction. Kind of a silly name begging the question as to whether there is power reduction or not? This was actually a post-PI MV with a few fixed settings. Reducing drive from the splitter to the output stage will reduce output power but not with any of the benefits that Power Scaling offers.
Apart from the loudness reduction without tone change, Power Scaling increases tube life by reducing waste heat off the tubes when the Power Scale control is set low. vvr will do this, too, except with a tone change. VPR will not change the tube dissipation any more than turning any level control in the amp does. EPA and any two-thirds approach will reduce waste heat from the tubes but not to the extent full Power Scaling can.
Similar to the splitter bias method, a cathode-biased output stage can have its power output reduced by changing the bias resistor value. The intuitive form uses a rheostat in series with a fixed resistor. With the pot at zero resistance, there is just the fixed Rk and maximum heat and maximum power. With all of the rheostat's resistance in play, idle power is reduced and so might be output power. We say "might" because the presence of a bypass cap here will maintain maximum power even with the reduced idle current.
Before Marshall introduced EPA, they tried a different approach called VPR, Virtual Power Reduction. Kind of a silly name begging the question as to whether there is power reduction or not? This was actually a post-PI MV with a few fixed settings. Reducing drive from the splitter to the output stage will reduce output power but not with any of the benefits that Power Scaling offers.
Apart from the loudness reduction without tone change, Power Scaling increases tube life by reducing waste heat off the tubes when the Power Scale control is set low. vvr will do this, too, except with a tone change. VPR will not change the tube dissipation any more than turning any level control in the amp does. EPA and any two-thirds approach will reduce waste heat from the tubes but not to the extent full Power Scaling can.
Similar to the splitter bias method, a cathode-biased output stage can have its power output reduced by changing the bias resistor value. The intuitive form uses a rheostat in series with a fixed resistor. With the pot at zero resistance, there is just the fixed Rk and maximum heat and maximum power. With all of the rheostat's resistance in play, idle power is reduced and so might be output power. We say "might" because the presence of a bypass cap here will maintain maximum power even with the reduced idle current.
