It just occured to me that the PF86 instead of a EF86 migth be a better choice for a low level preamp because the 300mA heater could be fed with constant dc current easely obtainable from 6.3Vac (the needed ca. 4,5V at the heater would leave nice headroom for regulation ). Did any of you use the PF86 instead of of the EF86?