This Post Has Been Edited by the Author
In Reply to: RE: update.... posted by vinnie2 on February 12, 2019 at 14:57:38
Many moons ago Mike Lafevre posted some operating points for a low voltage 845 tube amp that he had seen in stereo sound magazine and had himself.
The operating points were plate volts 430vdc, plate current 62mA, grid volts -51vdc, with a 5k loading. He said it sounded great to him. I liked the idea the idea of the low voltage so I breadboarded one, and that is where the above schem came from. The only problem was I never hit all his operating points, and putting it together again yesterday I found I still haven't. The strange part is it sounds pretty good, but I can't help but wonder jhow it will sound with MIke's numbers. As it stands now I have plate volts 370vdc, plate current 64mA, grid volts -19vdc and loading is 5k. I can adjust the B+ voltage, but it is the grid volts that have me puzzled. If you look at the plate curves for the 845, at 370 vdc plate volts and 64mA current, the grid volts should be somewhere in the area of -40 vdc. I want to try and hit Mike's magic numbers, but I know this is a can of worms because when you change one thing the others change with it. Does anyone have a system they use for zeroing in on a set of operating points, or is it all trial and error?