Biasing a Marshall JCM 800 2205 Amp with a simple multimeter! Pin 1 and 3??

[lowell]

I think it's a pretty common misunderstanding, especially with the internet and forums etc, that someone reads something about -40v on the grids being correct bias. Well, for a given specific amp, biased by the factory, who sells after market tubes that have ALL been matched to operate well at that -40v grid voltage. That could easily be misconstrued for bias current. Which is what we're really after when biasing tubes.