Marshall fans, I have 59SLPRI (2006?) and have recently had the original tubes replaced (via an amp tech) to Groove Tube EL34's. Does anyone know what Marshall used for the stock tubes? The old tube reads: Marshall EL34 VLVE-00042 22/06 Chinese? Russian? Sovtek? Mullard? I ask because I was considering trying the Mullard Re-issues and wanted to make sure that Marshall wasn't using these Mullards in their amp re-issues under the 'Marshall Name". Having said all this (and I haven't pulled the amp from the cabinet yet) can you tell me where the bias adjustment is located in the amp/chassis? I tried Marshall's site, but couldn't find the info. Thanks, guys.