Because VT4c-211 too hot so I design a water cooling platform to setup TUB.
Second hand GE VT4C-211s .
Top view. The cooling heatsink is close rear but no contact case.
Rear view. I open a window for water pipe through.
Another cooling platform view.
Finish 6C45pi and 211 cathode bias voltage.
For tone color issue to fine tuning 6C45pi and 211 cathode's capacitors.
Change 211 cathode resistors and mount cooling platform too.Because too hot.