Mesa tube matching . . . need a tube guru !

[Cedrik Menard]

I recently swapped out a pair of power tubes in my 2:90 during a troubleshooting process. The octet of 6L6 that was in my unit when I bought it was of Red colour code and they are labeled STR430. I replaced an (appearently) faulty pair of power tubes in channel A with Green colour code and they are labeled STR440. Now the scratchy noiseI had on A side has dissapeared but I noticed that to get equal rehearsal volumes on both sides I had to set the A side volume @ 1 o'clock while the B side (unchanged tubes) was @ 12 o'clock. How come? My 2:90 is only 2 months old and I used Mesa replacement tubes. Is there any risk of damaging the amp by using mismatched tubes? why is my volume unbalanced now? Thanx for your great support!

Cheers!

 

[Boogiebabies]

There are two output transformers in the 2:90. The imbalance may be due to the output of the the bank of tubes you replaced. Not all tubes of even the same make put out the exact amount of power, plus the different color codes bias themselves a bit differently and may have an effect on total output power. Since there are two power sections, no harm should come to your 2:90.