I’ve had the BHK 250 for almost a month now. There are several threads but this seems as good a place as any to put some thoughts.
First, the BHK continued to improve for over 300 hours; that 100-hour break-in mentioned in the manual really needs revision.
The BHK is without a doubt the most refined, subtle amp I’ve ever owned. It reveals small inflections in a singer’s voice or a player’s articulation that show exactly what what’s going on and draw me in to the music. This quality of the BHK was evident from the moment I put in my system. As the amp settled in, I became particularly impressed with the way it clarifies complex music, like a full orchestra. I can hear more deeply into the music than I have ever been able to at home. Bass is better controlled and perhaps a little more extended, and soundstaging is better (within the limits of my weird room).
All was not perfect, though. For several years I ran a bi-amped setup with a tubed amp (Golden Tube SE-40) driving the midrange/tweeter section and a sold state amp on the bass module. This setup was very musical and enjoyable, although not the ultimate in resolution. With the BHK in place, I admired the clarity and generally enjoyed the music very much. I could not identify any particular aspect of musical reproduction that was lacking, but something still didn’t seem quite right. I thought that I had gotten so used to the slightly euphonic coloration of the SE-40 that I just needed to get accustomed to a more neutral-sounding amp. Yet sometimes I still missed the tube amp, which did not seem to make sense.
Two days ago I put in a set of Tungsram PCC88 tubes that I had purchased but held off installing until I felt that the BHK was completely broken in and I had a good handle on its sound. As it turned out, I wasn’t wrong in thinking that I wasn’t getting the best of the BHK. From the moment I installed the Tungsrams, the sound relaxed a little and instruments sounded noticeably more like themselves, while the overall clarity remained. With the stock tubes it seemed as though an oboe sounded like an oboe, but the Tungsrams showed that there was real room for improvement in instrumental timbre. I would guess that this has to do with better reproduction of harmonics. The Tungsrams are both more accurate and more enjoyable, at least for me. Soundstage depth was also better and there was a little more bass.
The above comments are based on listening through my DS DAC/Bridge II combo, with source material ranging from redbook CD through DSD. The BHK sits on a PowerBase (used just for isolation, since I have a P5 to power the system).
The BHK amp is a masterful design and deserves all the good things that have been written about it. The takeaway from my experience is that tubes clearly do matter. With the upgraded tubes I am getting the kind of sound that I hoped for when I decided to go for a BHK 250.