Another poster pointed me to this review of the BAT VK-51SE tubed preamp
in Stereophile:

http://www.stereophile.com/amplifica...at/index4.html

I believe figs, 1 and 2 were swapped. In other words, the caption for
fig 2 actually applies to fig 1. Has anyone noticed the frequency
response at high gain in fig 1? It's down about 3 dB at 7 KHz (!) at a
gain setting of 17 dB. Note also that the left and right channels are
different by about 0.2 dB in gain. Moreover, when driving 600 ohms,
which is one of the spec'd loads I guess, the low frequency 3 dB point
is at 100 Hz!

These are not very good measurements for a preamp. Of course, it
received glowing endorsements .