FWB Filtering

[MarshallPlexi]

Does a Full Wave Bridge require less filtering than a Full Wave Rectifier? The reason that I ask is because on a 50W Plexi with a Full Wave Rectifier, Marshall uses a 100uF cap for the plate supply and on the 100W Plexi with a Full Wave Bridge, Marshall uses a 50uF cap for the plate supply.

Does this mean that the FWB needs fewer uF of capacitance in order to achieve the same amount of filtering?

[Chris / CMW amps]

Does a Full Wave Bridge require less filtering than a Full Wave Rectifier? The reason that I ask is because on a 50W Plexi with a Full Wave Rectifier, Marshall uses a 100uF cap for the plate supply and on the 100W Plexi with a Full Wave Bridge, Marshall uses a 50uF cap for the plate supply.

Does this mean that the FWB needs fewer uF of capacitance in order to achieve the same amount of filtering?

Full wave is the most efficient way of rectifying.

Regarding the differences in filtering between pre '84 50 and 100 Watt Marshalls: both do have their own "qualities". Just use your ears and experience "the feel" and see what you like the most.

Hope this helps.

[MarshallPlexi]

Well since a FWB is twice as efficient as a FWR, I was wondering if it needs half as much filtering to deliver the same punch. Here's why I wonder this.

For a FWR, the DC voltage has a break in the sine wave because for half of the time the diodes are not conduction so the waveform would look like this:

_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_/\_

Whereas with a FWB the sinewave would look like this:

_/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\_

If I am viewing this correctly, it seems logical that it would take less filtering with a FWB to equal the same filtering as a FWR with double the cap value.

Am I totally off base here?

[Enzo]

But your waveforms are not correct. With two diodes and a center tapped transformer, the two ends are opposite polarity from each other. SO EACH end shows your upper waveform. But they are then connected together, and since they are 180 degrees out of phase the result is the exact same waveform as your lower example. In other words, you get 120 pulses per second from either system. That is what the FW means, full wave. Your upper waveform would be HW half wave. Half wave is what for example Fender used for decades in the bias supply.

The performance is the same for filtration. The difference between the two systems is the transformer: you either split the winding and ground the center tap and use two diodes, or you use a simple winding with four diodes. In other words do you want to specify a 360v transformer and four diodes or a 720v CT transformer and two diodes.

[MarshallPlexi]

You're right....You're right.... I forgot about about the half wave rectifier. I knew I had seen that somewhere before.