Russ,I do get it.I am merely going by the info the guy gave us.First,he is not using Mesa or GT's,he has JJ's- if they are in the right "zone" as far as bias is concerned it is pure luck.As you say the values will change from tube to tube even in the same production run,which is exactly why,if you are not using Mesa or GT tubes which have been put in a circuit and graded before you buy them,you have to reset the bias for the tubes you use.In the example you give with your JMP I have to assume your output is biased properly,in which case of course every speaker change or pre-amp tube change is going to make a difference.Look, I agree with the fact that speakers make a big change in tone,assuming everything else in the amp is up to spec.It is almost impossible to diagnose an amp this way,without having the amp on the bench in front of us,but based on the symptons and conditions he gave us,his clean channel is good but he aint getting the bite or edge on his lead channel,I still got to think his power tubes are underbiased and no matter what speaker he uses he aint gonna get the "balls" if his amp aint biased right.The speaker can only give you what the amp gives it.I do agree with a lot of your points but again you are assuming he has the right power tubes working.If he walked into my shop with the same "complaint"before I started trying to sell him new speakers I would open the amp up and check his bias first then pre-amp tubes and if they were all up to spec then you have to suspect a speaker change,you see what I'm saying?My feeling on the whole Mesa grading system is that it is a way to sell more tubes under the guise of making it easier for the average player to change his own tubes without having a tech set the bias.I have found that with their system the tubes are ,at least all the Boogies I've serviced,biased way to cold just to keep things safe.I have only used the Mesa tubes in my own amp once,probably 20yrs ago in my SOB.I then modded the bias circuit on that and my IIc+,and I aint saying the tube itself was the problem,but it just wasnt biased to my taste.If somebody brings me an amp that doesnt have an adjustable bias pot to be retubed I will install it for nothing,that is how important I feel it is.I'll admit I am pretty anal when it comes to biasing,I have 14 amps that me and both my sons use,and I spend a lot of time checking the bias,you would be surprised at how much it drifts as the tubes age.Anyway,until he either gets the "right" tubes from Mesa or GT or has the bias checked I still gotta think chasing speakers aint gonna do it yet.