K&K Audio / Lundahl Transformers: opinion needed about raven style preamp. by papageno

hello.
i built raven style preamp ( pp preamp with input and output transformers)
input is lundahl 1544a and tube is 6n1p , output transformers is lundahl 1660 pp
i applied ccs to the cathode leg of 6n1p, so it is differential and output transformer coupled pushpull transformers.
plate voltage of 6n1p is around 200v, and current is 10ma each triode section.
i wonder if my choice of 1660 pp for 6n1p is good or not.
because i see much deterioration on the output signal on the oscilloscopic pictures.

at the moment, i soldered 3k ohm resister across the secondary of 1660 pp .
this improved the signal wave form. sonically, became darker and heavier.
but without this loading resister? , the signal waveform isnot good shaped as inserted signal wave.

if 6n1p is not good choice, what tube can be good candidate for 1660pp ?

best

kim