A rectifier tube with "traditional vintage sag" and a compressed feel.
The Mesa/Boogie 5U4GB rectifier tube is among their very best overall 5U4 and their tube of choice in the production of all Mesa/Boogie amps that feature this tube. Based upon classic 1950s technology, the 5U4GB is a vastly improved 5U4 design that is extremely reliable and consistent, as well as much more compact. This tube produces a "traditional vintage sag" with the most elastic and compressed feel of the two 5U4's that Mesa/Boogie offers. The 5U4GB short version has an amazing feel and exceptional overall quality that make it Mesa/Boogie's factory favorite.