• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

KT instead EL

You probably want a B+ of 400V. Bias at 50mA may work but you might want to go higher. The OPT primary shown is 3.2K. I think that may be a little too low for a KT88, 5K might be a better choice.

Also the KT88 is a tetrode so you won't have the wire from the third grid to the bypass cap (C5). Also you might want C5 to be a higher value.

I'm not sure about the resistor in series with the UL tap. My SE KT88 doesn't have one there.