pulling the power tubes is going to raise voltages in the preamp and the filter caps should be rated for the increase. but pulling the power tubes should render the power amp section dead, but if it is not shunted to ground it can produce noise with some of the components still "in circuit". a schematic is always helpful when seeking advice on do's and dont's of the gear in question.
Disclaimer: I make and sell Buffers. I also sometimes Modify, Build and sell preamps and amplifiers. My opinions are not intended to be sales pitches. I am a one man shop and prefer to spend time with my wife and family, i work full time on call and love to spend my spare time doing other things. I only make, modify or build things for those that seek them.