The DR201 switched to KT88 in the early 70's I believe...
MHuss Hiwatt Amplifier Pages - Detail Views
https://www.premierguitar.com/articles/22263-ask-amp-man-taming-a-hiwatt-dr-201
"According to schematics I’ve perused, Hiwatt apparently produced two versions of the DR-201: One with six EL34s in the output stage, the other powered by four KT88s. Theoretically, the four-KT88 model is more capable of producing the 200-watt stated output than the six-EL34 version, which would probably be closer to 150 watts.
But I don’t believe either configuration actually produces 200 watts of continuous power. The power supply design in both amps should be identical, and while the stated 650V DC plate voltage should be more than ample to support a 200-watt amp (given enough current capability), the power supply only provides 410 volts to the screen grids of the tubes."