6H30PI Preamp Vacuum Tube, Single

They greatly upgraded and improved the sound of my Audio Research preamp

I bought a pair of these from a friend for $50 that I used in my Little Dot MK II and they really did increase the amps output over the default tubes from China. I also ended up using the RiverStone Audio GE driver tubes sold here in matched pairs for only $25. I spent a lot of money buying other tubes, both for power and for driver tubes to roll with my L.D.MK II. So you can get great overall sound by buying the tubes I ended up keeping (About $80 worth) So $150 + the $80 for your N.O.S. tubes is only $230! Try getting a better all tube headphone amp to use with my Sennheiser HD 650's.Headphone amps usually cost much more than $230 for the all tube version of the up-graded Little Dot MK II easily matches or even surpasses the more expensive Little Dot tube amps. The best Class A/B Solid State headphone amp I found was the Emotiva A-100 Amp/High output headphone amp. You get 1.3 watts or 1,300mw into a 300 Ohm load. WOW! be careful not to blow your headphones by knowing where the volume knob is set at. I used a white line decal to mark the output.