So I checked and re-biased my DSL 40CR last weekend. Very easy to do with a simple ohm meter. When I checked bias 1 tube was at 35.1 and one at 31.4mv. Based on posted I have read here I know the range is 28 to 40 with the general guideline around 35- but let your ears decide. I also read on a different forum that not setting both tubes the same ( but within spec) yields more " harmonic content". I found around 32mv to be where I liked it, then set one tube to 34mv and left the other at 32. It "seemed" to have more complexity mis-matched , but maybe that is what I wanted to hear. Anyway, is a mis-match in bias within specs okay for the amp and tubes? Mine was when I first checked and it has survived but just seeing if there is an opinion. Stock tubes by the way with the exception of the Sovtec LP 12ax7 that went in the PI slot once I settled on bias. It sounds better with it, just a tiny bit smoother and maybe took a tiny bit of the edge that some don't like in the amp away. If you have a DSL and have not tried biasing, I recommend it. It's easy and if you stay within the range suggested by Marshall it is another way to find something new in your amp. If nothing else you'll know where the tubes are set now for reference later.