@divertiti , I've been listening to the Cossors on my LM508 for a couple of weeks now, biased at the LM suggested 120ma. Naturally this post grabbed my attention.Have you seen an advertised bias current for the Cossors? The testing data sheets for all 4 tubes say measured - 60ma at the specified plate voltages. Spec or QA test results for matching pairs?
Target bias dictated by amp or by tube?
If my amp's (Line Magnetic 508ia) manual says to adjust bias of each power tube to 120ma on the front meters, but a set of after market replacement tubes (Cossor Valve 508) state their bias should be set to 65ma, which stat should I be following when putting in the new tube?