In this section will be taken into examen the common topologies used for  the rectifying functions. Audio designers involved in tubed-amp designs can benefit of many choices based on solid state, vacuum tube and hybrid solutions. The results are presented in synthetic form for a quick evaluation. At the end three summary table are presented.

Test Conditions:

1. Vin_rms = 220V_rms
2. Freq = 50 Hz
3. Current Load = 50mA
4. Capacitance = 33 mF
5. Vacuum Diode 5U4-GB
6. Solid State Diode 1N4148

Parameters under Evaluation

1. Voltage Conversion Efficiency (VCE) measured as Vout_rms/Vin_rms
2. Diode's Pulse Current Spectrum
3. Ripple (V_pp)

SS Wheastone's Bridge

VCE = 1.36

Ripple = 13.61V_pp

Diode's Pulse Current FFT

VT Wheastone's Bridge (3 Tubes)

VCE = 1.07

Ripple = 24.47V_pp

Diode's Pulse Current FFT

VT Wheastone's Bridge (4 Tubes)

VCE = 1.24

Ripple = 11.148V_pp

Diode's Pulse Current FFT

"Classical" VT  Rectifying Circuit

VCE = 1.17

Ripple = 10.45V_pp

Diode's Pulse Current FFT

Hybrid Bridge

VCE = 1.36

Ripple = 13.61V_pp

Diode's Pulse Current FFT

Summary

Fig. 1 VCE for the examined circuits

Fig.2 Ripple values

Fig. 3 Load capabilites of different topologies

Conclusions

    The hybrid bridge results in the best trade-off  between electrical and sonical requirements. This wonderful topology keep off also the requirement of a center-tapped power transformer and permits the easy solid-state-like production of a contemporary positive and negative rail. On the contrary pulse current FFTs have the vacuum-tube imprint.