At the beginning of this hackaday project, I did not know well about vacuum tube amplifier. But now I've made and designed several things, including radio (reflex, super-regenerative, superhetrodyne..), amplifier (subminiature, type-19, type-38, 6SN7, 14GW8) and got to know what's vacuum tube, and how wonderful sound can be generated by it. So now I would conclude this project with this 14GW8 vacuum tube stereo amplifier. The output trans is modified cheap autotransformer and the plate voltage is directly generated by rectified AC 100V. The heater voltage is simply obtained by DC 15V switching AC/DC adaptor. Through this project, I got to know vacuum tube circuit is not black magic but it is surely working if properly designed. I had a knowledge of transistor circuit (and to tell the truth, I've had a course for more than 20 years at several university), and I got to know the basic knowledge is exactly the same between transistor and vacuum tube. (except for heater voltage requirement..)
And the above movie shows the operation of single tube (for each channel) stereo amplifier. The 14GW8 surely has a very high gain, and it is quite useful for simple audio power amplifier!
Thank you for interest!