I do not know if R17 / R27 need changeing. Your 6.3 volt filament supply needs to be able to deliver the extra current. If I am not mistaken you will need 1.9 amps for each kt120 plus .3 amps for the 12AT7, plus maybe a bit of margin.
I currently use a pair of KT120s with an Edcor power transformer with sufficient current. I also have adjustable bias resistors and have them set to their highest current setting. They sound quite good and add some weight to the music when compared to 6550s and EL34s.
Nate
Nate
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