The way I do it on my ST70 is I first measure, and turn down the bias adjustment. Then I swap the tubes, measure, and turn the bias back up to the correct operating point with the new tubes.
This makes sure you don't se the bias too high. Also, recheck the bias, and readjust it once the amp has warmed up, and again a few days later, as the bias will change after the new tubes have been heat cycled a few times.
John C.
This makes sure you don't se the bias too high. Also, recheck the bias, and readjust it once the amp has warmed up, and again a few days later, as the bias will change after the new tubes have been heat cycled a few times.
John C.