Be careful here... Check the specs before you operate power tubes under load at less (or more) than the rated filament voltage. Depending on the filament type, many seem to require +/- 5 or 10% on the fils to prevent damage to the tube. - Mike > And it was always good design practice to derate the filament voltage 10-15%. Try type 10 tubes or > the larger triodes for class A amps. I need plans for a center-fed TC. > > zeke