Atma-Sphere in CO?

while we can test the tubes, that may not really give you the information you are looking for, we can test to see if it is working, and get some idea of the condition but this won't tell how it sounds or how much use they have had. In addition, this would also take quite a bit of time to test that number of tubes.

What you want them to do is test the 6SN7s. If they are good, that helps a lot! They should not be borderline. Don't have them test the power tubes, instead you can do that quickly by comparing them to the photos at this link:http://www.atma-sphere.com/Resources/6AS7G_Visual_Inspection.php
The reason is that if the tube is failing, quite often it knocks out the link or links in the photos. So a tester really isn't needed- the amp has a meter, if you are concerned about strength, and it can be used to get a relative merit reading of any power tube.

@brownsfan & @atmasphere great, thanks for the information. I'll do some checking, swap out some of the 6sn7s for some nos ones I've got around, and do some more listening tonight.

How does the dynamics compare from the M60 to the 300B?

On the DIY Forum someone changed the Vcaps to another brand i forgot. The sound was tonally warmer.

@phantom_av Unfortunately it's been too long for me to give any reliable information.

I've transitioned to simple source follower amplification (first watt f4 mono-blocks, only adding current to the signal) and focus on getting the warmth from my preamp (Don Sachs 6sn7).

That combination is remarkably beautiful with great tonality and an amazingly holographic soundstage.