Marshall Powertube Question

[braintheory]

I have a 50w 2204 set up for 6550’s/KT88’s. Tried one pair of my Chinese KT88’s at the minimum bias setting and it measured 62mA. Tried a pair of JJ 6550’s, again minimum bias setting and it measured 39mA. Would I be able to just pop in EL34’s and bias them or would my tech need to change something to make EL34’s run properly in it?

 

[jasonP]

Typically, Marshall would use like a 82k bias splitting resistors vs 220k for el-34's and the negative feedback wire would have been moved to a different speaker tap as well as a different bias dropping resistor to give you more range on the bias pot. If you opened it up and took a picture a guy could confirm on what would need to be done.