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I have two band new UA LA-2A, bought two sets of GE LP 12AX7 pair + RCA 12BH7, that were vintage new and matched and switched the stock LA-2A tubes out.

Was there a difference?

I used a Neumann M 149 into an SPL Premium mic preamp (which conveniently has two outputs per channel, (a cool parallel setup).

I did a comparison between one LA-2A with stock tubes and one LA-2A with the GE LP.

At first I felt the stock tubes sounded close. After a few minutes zoning in on things, I started hearing how these tubes have a silkier high with a more pleasing mid and fuller lows.
The stock LA-2A sounded just a bit edgy, compared. Not quite as hifi.
Don't get me wrong though, if I hadn't switched these out, I'd still be in love and should and when these new tubes die, both my stocks LA-2A 's are to die for. I have backups tubes now but oo la la... these new tubes are staying!

Comparing both LA-2A's after both sets installed, sound so close I trust they were matched very well. Thank you Christian from ProAudioTubes. You were extremely helpful and very interesting! I will be calling you for more tubes.

I'm happy to report, tubes do make a difference and these GE long-plate 12AX7 on the output with the RCA 12BH7 sound great! They are also very quiet and not even broken in.