Power Transformer & Rectifier
Winding sag at this load
How it works
A full-wave rectifier flips the negative half-cycles of the transformer secondary upward, producing pulses at twice the mains frequency. The reservoir capacitor charges to the peak of each pulse, then supplies the load alone until the next pulse arrives, sagging as it discharges. That sawtooth sag is the ripple.
Valve rectifiers have a large, current-dependent voltage drop (15–20 V for a GZ34, 40–60 V for a 5U4 or 5Y3) and produce the gentle "sag" prized in vintage guitar amps. Silicon diodes drop less than a volt, so the same transformer gives a noticeably higher B+.
The waveform plot is a time-step simulation: the capacitor discharges at a constant load current (dV/dt = −I/C) and is recharged whenever the rectified sine exceeds it. Real transformers also have winding resistance, captured roughly by the regulation percentage.