The boogies are about a 4/5/6 on the Groove Tube scale.
The is a pretty simple mod that can be done to make the bias adjustable.
Mesa does very good matching. They have six color codes that all fall within a range of a good spec tube. Mesa needs to keep a tight range as their grid biased amps have a fixed bias and therefore expect a tube plugged into the amp to be a tube that meets design spec as tubes did "in the old days". Their color code is as follows: Red, yellow, green, gray, blue, white. The cross reference to GT stuff is that all the Mesa tubes fall into a GT 4-6 range with red and yellow bing a GT 4, green and gray being at GT 5 and blue and white being a GT 6.
GT would take tubes that had problems such as improper test results from being assembled wrong or whatever, tubes which fell outside design range and put them into their low range (1-3) or high range (8-10) and put something of a marketing twist on things describing that a low tube (weak tube) would break up sooner (of course ... it was a weak tube out of spec) and was best for folks that wanted a strong amp to distort sooner. High number tubes (8-10) were best for clean players, jazz or bass as they stayed clean longer. Unfortunately, these out of spec tubes even when properly biased could and generally would exhibit problems more quickly than a tube that was assembled properly.
On Mesa tubes I prefer the blue and white color codes as they are generally the most close to design spec. of the tube type.
