Atma-Sphere MA-1 tube rolling

One more troubleshooting note: I had an awful buzzing/loud humming coming out of one of my Sound Lab speakers. I switched MA-1 monoblocks, and the buzzing switched to the other speaker. Then I proceeded to replace all the output tubes, first seven on one side, then seven on the other, and tested after each replacement. The buzzing was still there. Next, I proceeded to replace the most posterior (sonically important) driver/gain 6SN7 tubes, but the buzzing was still there. Lastly (almost) I replaced the main driver tube, which is in front in the Mk 3.3 model, and the buzzing immediately stopped. I was most surprised that this was the failed tube, as it was a new tube, with less than 30 hours on it, and it was a modern Tung Sol 6SN7 GTB. . . so it appears that currently Ralph’s suggestion to stay away from the Russian 6SN7’s seems to be rather accurate.

I was most surprised that this was the failed tube, as it was a new tube, with less than 30 hours on it, and it was a modern Tung Sol 6SN7 GTB. . . so it appears that currently Ralph’s suggestion to stay away from the Russian 6SN7’s seems to be rather accurate.

If you look on our website you'll find this warning, which has been there for nearly 20 years now

NOTE REGARDING SOME TUBES
We have seen on-going problems with 6SN7s marked as "Sovtek" and "Electro Harmonics" More recently we have seen similar problems in reissue tubes marked "Tung Sol" and "Mullard". We do not recommend these tubes in our products. While they will not damage our products, neither will they perform optimally or reliably. If you are experiencing a problem and any of these tubes are installed, replace them first before doing anything else.

@atmasphere:
Thanks for the reply.  I must admit, I haven't read much of your website, but only the instruction manual that came with the MA-1.  
The amplifiers are a phenomenal match for the Sound Labs.  I'm enjoying them immensely.  Thanks for your great work! 

Hello Ralph (@atmasphere),I'm posting this here so others can share your response; apologies if there is a more appropriate place to ask.I just bought a pair of M-60s, built as II.2s but upgraded by you in 2008 with a PS boost; they have just one switch and one pot on the front.  I cannot get the output to null on either unit, so I am wondering how to proceed.  I checked all output tubes for blown tiny fusible links near the base, and indeed found one ( but only one ) bad tube.  Even if I remove a tube from the other side of that unit, output will still not zero.  On both units, I have to turn the pot fully CCW to get a minimum.  On one unit it's down pretty close to zero, on the other one closer to mid-scale.So:  1) is it safe to run the amps unbalanced, at least for a little while?2) without a tube tester, how do you suggest I find bad tubes?  For example, could I start with just one tube on each side and juggle tubes until I get a balance, then try for 2 on each side, etc?Thanks!

@crowdaddy2

Insofar as I know, the best way to find a failed tube is trial and error:  you should have a second full set on hand anyways.  If replacing all the tubes doesn't work, send back to manufacturer for check-up.  Ralph and Atma-Sphere will be glad to evaluate the problem.  I don't think anyone can really tell you what the problem is without physically evaluating the unit.  

Best wishes!