None (pure triode mode) – but option for 6dB of cathode feedback via secondary winding.

The TL783 or LR8 can only dissipate ~3W without a heatsink. For B+ above 350V, use a dropping resistor (5kΩ–10kΩ) before the regulator to offload power.

Original Xin Zhi Zhao schematics used 0.22µF/630V coupling caps between driver and output stages. The updated version recalculates the low-frequency cutoff based on the output tube’s grid-leak resistor:

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