I'd love to try the new KT77's. My only problem is that VTL doesn't
recommend anything that they haven't tested and proven in for a comfortable
period of time. They say stick with the EL34. Is the KT77, in most cases a
drop-in sub for the EL34 ? What possible problems could I be up against? If
the tubes will bias up @30ma like the EL34's and appear to look and sound
correct , is there any further danger ? I wonder if the bias will still be
30ma for the KT77's ? Any help will be appreciated , as I've heard that the
KT77's are an incredible tube [ better power and bass, clearer mids, and
still the same sweet treble of the EL34 ] . thanks

All my literature shows the KT77 as a drop-in replacement for the 6CA7
& the EL34.

http://www.nostalgiaair.org/

Will help you with electrical data and substitutions. Most of the data
you seek should be there, and if not, Rich Lancaster (the owner of the
site) is incredibly helpful if asked.

Yes, you need to re-bias whatever tubes you use, when changing tubes
unless your unit is self or fixed bias.

Peter Wieck
Wyncote, PA