Atma-Sphere MA-1 tube rolling

@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!

I swapped tubes between sides until I got a good null on each unit.  As advertised, the M-60s do sound great:  most noticeable immediately was better localization of sound sources. 

Will take a gamble on some $20-a-pair jugs from Ukraine; perhaps if I precondition them they will last a while.
Am thinking of building a uTracer:  https://www.dos4ever.com/uTracer3/uTracer3_pag0.html
Very clever tube curve tracer, over 1800 built so far.

I had good luck with Ken-Rad VT231's in my MA1s. Cheers,
Spencer