The two 12AU7 (5814) are closer to the center and the two 12AT7 (6201) are closer to the transformers. The circuit for the later version is the same as the earlier version, just laid out differently on the boards. Try using a 12AX7 instead of the 12AU7. The preamp sounds better that way, IMO. It will have more dynamics and life. The design is basically a Dual Mono Marantz 7 with a very stiff un-regulated dual mono power supply. I used to own a Marantz 7 and the VTL is way better. Not even close. Another Marantz 7 variation which is even better that the VTL is the Perfectionist Audio Components (PAC) Pro-Reference IIB. It has a fully regulated monster power supply and is the best 12AX7 type preamp that I have heard. Both the VTL and the PAC have refinements in the audio section that make them better than the Marantz, but when you add the improved power supply too, it is not even close.