Whats on your turntable tonight?

Brian, all I can think of (also, a newbie in the world of tubes) is there is a mismatch.  Maybe they were well matched to begin with, but over time one of them lost its potential and the other was just fine.  Tubes are best when purchased in pairs or quads (depending on one's need) and after being tested and matched by the seller.  I know that Upscale Audio does that and most likely so do other quality tube sellers.  Anyway, that is my best guess.

Got back from Mammoth Mountain last night.  A fabulous week of skiing.

Atlanta Rhythm Section - A Rock And Roll Alternative  

Annie Lennox - Diva   Man, this is a wonderful album, both musically and sonically.

Albert King with Stevie Ray Vaughan  -  2 disc set, 45rpm Analogue Productions.  This is a piece of musical history.  And WOW, is it great!

@mammothguy54 

Yep Joel, what I was thinking too, but, the two NOS Brimar 12au7’s were matched from Upscale. So I have a good feeling they were sold as a good matched pair.

As I understand, a preamp typically isn’t as sensitive to matching or bias as an amp would be. Thus, unless there is a catastrophic failure, or an extreme mismatch, as far as I know, there should not be a significant difference.  

Curious.

Hey Brian,

Are you able to take any measurements of the 12AU7 tubes or check cartridge azimuth?  

Weird it didn't follow channels though...

@boxer12 

Tim, I have no equipment to measure tubes. Thought about azimuth, but again, after swapping the two 12au7’s, everything seems to back to ‘normal’. Haven’t checked in a while though, so could not hurt regardless.

I wonder if the Hagerman has some type of self-biasing circuitry and just flipping them allowed to be ‘readjusted’. I dunno.