Power supply unit

There are a few power supply units required for T8:

the transformer that provide the 550V, it is specified to be a 200V, 100ma transformer, however you would expect a significant voltage drop and I chose a 430V, 40VA transformer and planning to use full bridge rather than voltage doubler. This spec gave me 520 at the end....

The negative bias supply reuired a 120V, 10VA transformer. I combined the two and order a 50VA transformer from LITE

Different from the original circuit, I also use a separate transformer for the AU7 and AX7 filaments. I use a 50VA transformer for a LT1085 regulated power supply. Some people believe using AC for filament can give a bit more dynamic but I am not sure if that's really dynamic of variability that one is hearing. From science point of view, using regulated DC can reduce noise and so used DC.

In order to protect the EL519, I also created a delay circuit to control 2 relays so that the +/- 170V is connected only after 40s and when the filaments of the EL519 are growing....

All these are placed on one single PCB