Change EL84 tubes on Eico HF 81

I want to change quad Mullard Russian EL84 tubes on Eico HF 81. I am new tube amp and I do not know much how to biaset EL84. Could you please give procedure or steps to biaset tubes?
I recently replaced quad Russian Mullard EL34 for Dynaco ST70 and sound is very good details with mid range and bass. For the price of $87 for quad EL34, this is wise investment for amp comparing to Mullard made in England costing more x5 for quad.