Bridge rectifier vs. two-diode rectifier?????????

[anson]

Hey guys,

I've got a 120 watt homebrew amp and am using a bridge rectifier for the HT voltage. My transformer has a center tap, but I used a bridge rectifier anyway just out of cenvention. Is there any advantage to using a bridge rectifier over the simpler two-diode rectifier seen in many amps???????

Is it more effecient, or safer? does it exhibit less sag? thanks for your help!!!
Anson

[R.G.]

Originally Posted by anson

Hey guys,

I've got a 120 watt homebrew amp and am using a bridge rectifier for the HT voltage. My transformer has a center tap, but I used a bridge rectifier anyway just out of cenvention. Is there any advantage to using a bridge rectifier over the simpler two-diode rectifier seen in many amps???????

Is it more effecient, or safer? does it exhibit less sag? thanks for your help!!!
Anson

If you left the center tap on ground and hooked the ends of the HV winding to the AC posts on the bridge, took B+ off the + output of the bridge and left the - output of the bridge open, it is EXACTLY the same in an electrical sense as a two diode setup. There is no electrical good or bad about it.

The only difference is that there are two additional diodes that take turns connecting the - bridge terminal to the then-unused half of the HV winding. As long as the - bridge terminal is unused, no good or harm happens.

If you connect something to the - bridge terminal, then the fun starts. That point is sitting at the negative mirror image of B+ but without a filter cap. Your finger touching that point would be very unhappy. So you now have a new dangerous point in your amp.

[Enzo]

I interpret the question different from the way RG did. I might be wrong, but...

What RG said was right or course, but it depends what you do.

If you ground the center tap and use two diodes, then you are rectifying half the transformer winding voltage. If you used a bridge the same way, the voltage would be identical, but you cannot ground the negative corner of the bridge.

Most amps that use a bridge are rectifying the whole transformer winding. The negative bridge leg is grounded and the + leg is the B+.

So if you have a 350-0-350AC transformer, grounding the CT and using two diodes - or half a bridge - provides 350VAC rectified. If you put a bridge on the winding and leave the CT not connected, you wind up with 700VAC rectified.

[Gregg]

I stopped using center tapped PTs long time ago. If you want a tube rectifier, then yes. Rest of the time I use toroidal PTs with a single HV winding + bridge rectifier.