I also bought this little bear B-1 hybrid amp looking for just that a hybrid portable amp. My one has the same problem with the power going into the tube filament. The original resistor should be 10 ohms and looks like a 2 watts one, but I take some voltage mesurements and something was wrong with it. So, I change it with 20 ohms 2 watts resistor and the voltage drop is very close the 6 volts needed for the filament. This was very important for the tube life and functionality. After this I just recharge the battery to full level and start using it. The amps is new and need more break in, but the sound is very interest for me. I like it more than the Fiio E07k because the warming tonalities. It really present a more tube like sound, not as flat as normal with the transistors. But the amp need attention, so it is not the buy now and used it for ever, no. This amp is more like a home made audio workshop proyect to play with.
I have no too much information about battery durability or good or bad performance because I just bought the amp yesterday and work yesterday night with the resistor problem. So, almost 2 hours of use on it. The volulme control generate scratch sometimes and it runs a little hot, not burn to contact, but hot. It is powerful enough to drive strong the Sennheiser HD598 and sound good with new Apple earbud. Like the soundstage presented with the new Apple earbud. You need to remove the headphones when power on or off because the strong switch clic sound and it is afected with the iPhone 4s EMI. This is rare, because the box is complete in aluminum and I guess this help shielding it, but something happen. Of course this only happen when the phone is using the network for accessing data, at least that is what I notice for now.
I drive it via Fiio line out adapter and direct from the headphone 3.5mm jack with nice sound results. The line out connection is better. The amps have a lot of power for my headphones. I never need to pass half the volume control position to listen strong my music with the line out connection. The sound presents hights limitations. I feel that the amps can not goes to the 20Khz normal response curve. For me it sounds like a 3 db drop beyond the 15khz, but I am guessing with this. Any way the highs are there, but attenuated. The mids range response is where the tube 3d sound stage magic present better. The musicians and sound separation is notable, not as wide as a normal tube amp, but the magic is present. The low bass also present problems. I can hear the bass, drums and chellos but not as tight as other amps here.
I am still learning it, knowing his capabilities and limitations. The power supply need more revision, the 20 ohms 2W resistor is working hot to the limit. I am looking to modify it with a pulse dc to dc converter. Some ideas and regulators are in the evaluation process, but this need more experiment and time to play with.
For me this purchase is a very good one. I know for sure that the amps need attention since new, so I do not regret the decision. That is what I was looking for a DIY proyect that is working but need some fine details to get better. The amps look very cool and the physical body shape is very confortable on hand. The sound capabilities are from normal to good with nice hybrid sound stage presentation that I really appreciate when listen to music. Solid state amps sound very clean but the sound stage 3d effect on the tubes make me very happy. This little bear is a very good in between point.