If the volume control is a 50K pot, perhaps try a control with a value of 100k or 250K. The issue, too, is if the preamp circuitry is optimized for a 50K potentiometer...which it may be. It also appears that there is a grid-stopper between the wiper of the volume control and the grid of the input tube. What is the value of that resistor, and could it be decreased without compromising the performance? Is the circuit unstable without it?
If the volume controls were expensive, replacing them for higher value pots may not be the most prudent way to deal with the problem. How far away from the Ultrapath preamp is the phono stage?
I'm curious about this, mainly because I think battery power has some serious potential for quiet, great sounding amplifiers. All the old tube radios I've restored use them, and I am doing continuing research on the availability and variety of battery-based power supplies. I've learned that quite a few others have used this rather old technology with great success.
Erik
