The pedal uses op-amps (often TL072 or similar) to boost the input signal before it hits the tube. This "pushes" the tube into saturation more effectively.
The pedal takes 16V AC and boosts it internally to roughly 300V DC. This "B+" voltage is what allows the 12AX7 (ECC83) tube to operate in its linear region, providing real headroom. Blackstar Ht Dual Pedal Schematic
Understanding the schematic is key to maintaining, modding, or cloning this beast of a pedal. ⚡ The Core Architecture The pedal uses op-amps (often TL072 or similar)
If you are looking at a circuit diagram, focus on these areas: Blackstar Ht Dual Pedal Schematic
Even when unplugged, large capacitors can hold a high-voltage charge.
A high-impedance stage that preserves your guitar's high-end before the gain stages.