• 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.

6K output transformer for 6L6 ??

Billy,

There is no best transformer for a given tube in a given circuit. There is an optimum load for distortion, there is an optimum load for power output... and so on.

Some 6 years ago, I designed an output stage using 6L6 for one of my friends. 4200 ohms was the load with low amounts (I cannot remember exactly how much) of feedback.

Usually, the higher the load, the better the frequency response and the lower the distortion and power output. It is really your choice. Is there any reason for you to consider a tetrode for a SE amp? You could avoid feedback using triodes.

Mohan