I just got the tubes in and tried them out. Compared to the standard Groove tube 12AX7R. The 12AX7M is balsy, clear well defined low end, decent tone, low noise if shielded properly. They have more gain than the standard Groove tube. Having said that..the 12AX7EH is a close second. Good gain, clear, nice well defined low end but not quite the balsy low end of the 12AX7M..close though...Good tone. Having said that the 12AX7EH is a better buy at 1/3 the cost of the 12AX7M. Which will I use...12AX7M since I have it. The EH's will be my back up. I bought 2 of each while CE Distribution had them at 1/2 off till Christmas.