I've had my BHK pre for 4 weeks now. I have installed the Tungsram 7dj8s last week. I love what I hear with these. Compared to the stock tubes, there's a more realistic presence, and I'm getting a kick out of being able to pick out individual saxophonists in a big band -- something I like doing when listening to a live band!
A question: under what circumstances would one change the bias jumper? I changed the voltage, but left the bias at the factory setting. Is this a correct configuration for the Tungsrams?
The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.
OK, so at 194 tube hours on my BHK Pre, I installed the Tungsrams purchased from Upscale (platinum and cryo’d) and set the voltage to 6 (it really helps to use a small needle nose pliers to mover the jumpers). Prior to the switch, I totally agreed with previous reviewers about the sonic magic of this preamp. The 6922 built on this–rounder, fuller sound, holographic sound stage, etc. However, I agree with JAH, the sound was a bit etched which made treble strings a little hard. I thought this was due to new (3 hour) tubes, but after seeing JAH and Bascom’s post on the current settings, I went back in and changed the bias current from the factory 4ma to 5ma. Bingo, hard edge gone, amazing what a 1ma step up in bias will do! I would recommend the Tungsrams (get them from Kevin at Upscale Audio) highly! So yes, Bascom, the Tungsrams are a significant improvement, in my opinion.
As a postscript, I have three audio sources; turntable, CD and Satellite Audio. I used the Satellite Audio (Serius XM, etc) for background music, but was blown away on how much better it sounds coming through the BHK. Actually have been snagged several times into sitting and listening. Amazing…