Hey Alex- no problem! Two things with DHT’s that are harder to overcome than with Pentodes are C Miller and also grid current. Most of these tubes aren’t linear unless you can drive the grid positive with a high voltage swing. Otherwise the top and low end suffers and is what most people think when they refer to a 300B (or other DHT) as "woolly in the bass", or "lacks high end sparkle but the midrange sounds great!". That’s where C Miller has its effect is on the frequency extremes. A 6SN7 cannot drive the 300B’s grid into A1 unless it’s in SRPP mode or is direct-coupled. It can still sound good but you’re not hearing the 300B’s full potential. On the KT88, I assume the 6SN7 stages were cascaded? In that case, I can imaging how two coupling caps and two stages could bring too much of a harmonic structure to the sound and become dull and lifeless. However if two stages of 6SN7 were configured in Mu Follower, Cathode Follower, or SRPP you could benefit from the lower output impedance to "swing" the grid of the KT88 better and avoid the overly complex harmonic signature. Best, Aric
