ST-70 & Swapping in 12AU7 driver tubes

I purchased the 12AT7 version of the VTA ST-70 kit in mid-2009. I alternate preamps - but prefer my tube based unit. The problem I'm having is that there's just too much drive into the amp. Essentially, I can't move the preamp volume control (of any of my preamps) much past the 9 o'clock position - about 1/4 rotation. And that's with a turntable as the input device. You can imagine how little vol. control rotation I have when the input device is a CD player! I want to use the preamp volume pot. in a more linear region - closer to the 12 o'clock position.

My Question: Can I experiment with using 12AU7 tubes on the front end of the ST-70 - but WITHOUT altering the 8 resistors on the circuit board?? I mean, will I harm anything by doing this? (By the way I have Bob's input attenuator control for the ST-70. For now, though, I prefer to work with the input tube configuration.)

Appreciate any feedback.

it won't hurt anything to sub the 12AU7 in there, it just won't be running at optimum parameters.
If you like the sound and/or gain situation better after trying it, then you can make some resistor changes.

I took your advice and swapped in 3-12AU7s for the stock 12AT7s. There is a small reduction in apparent volume with the preamp Vol. control at the same setting as with the 12AT7s on the ST70 board. To be honest, though, the change is fairly minimal. The preamp Vol. pot might now be at a point a little nearer the 10 o'clock position versus 9 o'clock before the swap.

My associated equipment is a Sound Valves VTP-100 preamp (all 12AX7s) and EPOS ELS-3 mini-monitors and a 10 inch powered subwoofer. This is all set up in an 11X14 foot room with an 8 foot ceiling. (The listed sensitivity for the ELS-3s is 87 db/1W/1M.)

I did NOT change the 8 resistors Bob Latino originally identified as necessary to give optimum results with the 12AU7s. Does the resistor swap give a further gain reduction at the ST70 input?

Thanks for the information. I still wonder whether the resistor change brings with it additional drop in gain beyond just swapping in the 12AU7 tubes. What are your thoughts?

Thanks Bob.