Audio Note Kit1 2014 Edition
8W Class A singleended 300B valve integrated amplifier. More details on ANK Audio Kits website.
INITIAL TUBES

ElectroHarmonix 5U4GB

Sovtek 6SN7GT

2 x General Electric JAN 5687 WB

2 x Shuguang 300B98
LAYOUT
MEASURES

Idle current (measured at pin 8 of 5U4GB): 200mA

Gain (at 1 kHz): 37.2dB (left), 36.7dB (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.55% (left), 0.51% (right)

THD (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.54% (left), 0.50% (right)
TUBE ROLLING 1  Sovtek 6SN7GT replaced by RCA JAN V231 "Grey Glass" NOS:

Slightly lower gain (at 1 kHz): 36.6dB (left), 36.1dB (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.55% (left), 0.52% (right)

THD (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.52% (left), 0.51% (right)

Significant improvement comparing to Sovtek tubes  deeper, more 3 dimensional sound stage, a bit more delicate high frequencies, overall sounds lighter, but also much more realistic, musical.
TUBE ROLLING 2  ElectroHarmonix 5U4GB replaced by Sylvania 5U4GB/5931 NOS:

Slightly stronger, better defined bass comparing to EH tube.
TUBE ROLLING 3  General Electric JAN 5687 WB replaced by TungSol JTL5687 early 1950s matched pair:

Left tube: 9.8mA/4800, 10.2mA/4800

Right tube: 10.8mA/4800, 10.8mA/5000

Gain (at 1 kHz): 36.1dB (left), 36.2dB (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.56% (left), 0.77% (right)

Excellent sounding tubes, huge improvement comparing to the stock GE tubes.
TUBE ROLLING 4  Shuguang 300B98 replaced by Genalex Gold Lion PX300B matched pair:

Both tubes: 64mA / 5.8mA/V

Gain (at 1 kHz): 35.9dB (left), 36.1dB (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.39% (left), 0.49% (right)
TUBE ROLLING 5  RCA JAN V231 "Grey Glass" NOS replaced by Sylvania 6SN7GTA "chrome dome" (made in USA, 1953):

Unfortunately RCA tube started buzzing after about 8 months of use and I decided to try Sylvania.

iP / Gm: 8.9mA / 2600 and 8.7mA / 2600

Gain (at 1 kHz): 36.3dB (left), 36.4dB (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): 0.46% (left), 0.33% (right)

First impressions: good, strong bass, great dynamics, a bit dry in the midrange, a little agressive upper frequencies, slightly sibilant
TUBE ROLLING 6  Sylvania 6SN7GTA "chrome dome" replaced by RCA 6SN7GTB "black plate" (1960's):

I didn't like the upper range with Sylvania, which sometimes could be quite harsh and sibilant, so I replaced it with this RCA tube.

Balanced triode sections, low noise and microphonics

Gain (at 1 kHz): TBC (left), TBC (right)

THD+N (at 1 Watt into 8 Ohms at 1 kHz, source impedance 600 Ohm): TBC (left), TBC (right)

Comparing to Sylvania it sounds somewhat slower, bass is less controlled, but with smooth, rich midrange, harshness is gone completely
LINKS

Schematic: pdf

Audio Note Kits: ANK Audio Kits

Tubes: Tube Depot, Langrex UK, Watford Valves, Hot Rox UK, TC Tubes, 6SN7 reviews
Last update: 22.06.2018.