Success! (mostly) and a weird observation.
The hum is now down to a level that is negligibly audible at my normal (loud) listening volumes. I have to concentrate to hear it -- and this is with no music playing. It is still there if I crank the volume knob with no music playing. But with the OPTs of my modded Kaiju set to 64 ohms nominal secondary output impedance, I never go more than about half way on the volume knob - so I am happy with the hum level.
The only problem is that I have no idea what fixed it. I restored the stock bal and vol pots and added a bit of different spacing between some of the wiring. I left the ground/chassis connection at T13 b/c I didn't feel like undoing the changes I made to the B+ filter. BUT, I realized that I previously forgot to reinstall the ground lift/filter thingy when I moved the ground to T13. So I rejigged the wiring at the T13 terminal strip and added the thingy there. So what reduced the hum? No idea. It might even have been a bad original solder joint - I doubt it (don't we all), b/c I was particularly fussy about making each joint as good as I reasonably could - strong crimped mechanical connections wherever possible, high heat and watched for the solder to flow like water ... and I took my time with the initial build instead of doing my usual marathon "getting it done tonight" session -- but you never know.
Now the weird observation: both tubes vibrate. One more than the other -- I think it's the one that measured highest for cathode bias - 10V versus 9.83V. I'll check in the next few days. Tubes otherwise look normal - no abnormal glow that I can see and neither gets particularly hot -- compared to the Kaiju. But I noticed the vibration as soon as I powered the BP2 on. And then kept my hands on the Kaiju 300Bs as powered up that amp -- no detected vibration -- at least until the tubes got too hot to touch. I am pretty certain the vibration is coming from the tubes. There's negligible to no vibration at the chassis near the tube sockets and zero vibration coming from the power trafo. (Addendum: after finishing writing this post I felt the tubes again - the vibration has settled down but is still there).
Finally, the important stuff: more listening impressions. It is truly superb with my modified Kaiju. I've got Fleetwod Mac's self-titled album playing now through Roon and I am way more into it than I normally would be. Since I'm still playing around with the volume control in my modded BP1, I can switch between TVC and BeeQuiet attenuators in that amp, which makes for interesting comparisons. Compared to the BP2, the BP1 w/ TVC is more precise/detailed but comparatively lifeless and the BP1 w/ BeeQuiet just sounds like a lesser version of the BP2. I might still give the nod to the BP1 w/ TVC for select jazz and classical recordings where I want to hear the timbre of every note, but otherwise I strongly pref the BP2. Amazing! I can't speak to how the BP2 compares to a stock BP1 since mine is so modded. So perhaps they're more comparable than my experience suggests. [Edit: and this is with the stock caps still breaking in. The BP1 has fully broken in fancy Vcaps coupling caps and film caps in the B+ filter -- maybe when the BP2 is fully upgraded and gets its own complement of fancy caps it will completely overtake the BP1. Can't wait to find out]
Man, oh, man, there's a very strong likelihood that I'll be rebuilding the BP1 along the lines of the BP2 this summer. I'll be setting up a 2-channel system for tv/movies and lower volume listening - so I'll have a use for both BPs, and will have found a permanent use for my 2 Stereomour IIs. Awesomeness!
[Edit: I should mention that I am using JJ 300B tubes previously broken in with the BP1. I haven't listened to them in a while since I now use EML 300Bs in the BP1 and Kaiju and had to tweak the filament supply to use them. But I recall finding the JJs really punchy (punchier than the EML) but a bit stiff and rough/sharp around the edges-- but not in the BP2 - the music is beautifully fluid]
cheers, Derek
