Question about Hybrid Tube/SS Bridge Rectifier

[makinrose]

Hello Makinrose

I do not believe there would be a difference in sound between the two power supplies as they both employ a valve rectifier.

The traditional design with a centre-tapped winding on the high-voltage winding has the standard dual-rectifier . The out is taken alternately from one side of the centre-tap through a single diode, so the loss and sag effect is related to a single tube rectifier.

In a bridge, were it all valves, there would be two valves in series and thus twice the sag effect and much lower output voltage. Replacing the rectifiers on the negative side of the bridge with solid-state diodes bring it back to a single tube rectifier sag and voltage loss. The addition of the solid-state diode in series with the tube adds insignificant voltage loss or sag effect. The wonder might be if the harder turn-on of the solid-state diode might alter the tone?

If one considers that there is a generously sized filter capacitor following the rectifier, it could be assumed there would be little impact for the hybrid rectification compared to pure solid-state or even pure tube. Also, as most members of this forum have a copy of one or more of the TUT volumes, we are likely to add that small series resistor between the rectifier and first filter cap that Mo. O'Connor suggests, as this tiny component adds multiple benefits, one of which is to filter the possible solid-state turn-on noise.

Do you find there to be a true sonic difference between the same amplifier circuit powered from a valve-rectified supply or one with semiconductors? Most players do not hear a difference, especially when invoking distortion. My impression is that most players believe they should hear a difference and claim that they do so they do not appear silly if others present claim to hear a difference.

Valve rectifiers are quite a liability in a working musician's amplifier, especially if it a combination amp with speaker. As KOC mentions, you can have the sound of the valve rectifier without having to suffer its mechanical  detriment to reliability. It is embarrassing when your amp goes silent because the valve rectifier vibrated out of its socket; worse if it breaks and there is no replacement valve or amp.

I'm not sure that's entirely accurate.  Dual rectifier tubes were used in some equipment to increase the current capability and reduce the sag. It's a common thing to pull one of the rectifier tubes from Fender's Low Power Twin to increase the sag effect.  In my experience sag or compression is most important in amp that don't have much in the way of overdrive in the pre-amp.  The smoothing effect is important to the feel of the amp for many players.  That is not to say that the sag needs to come from tubes but there is definitely a difference in feel with an amp under relatively clean or semi clean tones with and without some sort of means to achieve sag and without.