I recently changed out the stock valves on my Douk Audio phono preamp with the GE5654 and still can't believe the difference its made. The stock valves were 6A2 and although they worked ok they just didn't bring any life to the music.
The preamp is a Douk Audio T3 ( budget pre amp ) and I am using a Shure Hi-Trac cartridge on a Thorens TD-160 mkII.
The GE5654 added a whole new dimension to the sound stage with vocal clarity, highs & midrange improving drastically. Instruments are much more defined and overall the playback is much more realistic and livelier.
They have being burning in now for about 40hrs and are still improving.
They have turned a budget preamp into something much more resembling an expensive preamp. Not quite as good as the Schiit Mani but definitely on the same racecourse. Very definitely a worthwhile change. Great service also from Audiophonics who always ship promptly.