Tube🌿Time on Nostr: ...For high dc stability, the difference of the emitter dc currents (378, 379, 380 vs ...

...For high dc stability, the difference of the emitter dc currents (378, 379, 380 vs 381, 382, 383), which is about zero, is kept constant by an automatic control loop including OP 303 and transistor 377. this loop is forcing i1 - i2 vi in the frequency range from dc to some hundred Hz. Trimmer 700 is adjusted for flat amplitude response in the take-over range of the direct drive via C536 and C537.