The basics of the rectifier diodes goes like this.
The full wave bridge configuration used in the CF amp means each diode is on opposite sides of the power transformer secondary. Refer to the schematic and you can see them being fed by the power transformer secondary. So they are seeing the same voltage waveform...but 180 degrees phase difference!
So on one side as one is going more positive, the other is going more negative. Diodes turn on as it goes positive and shut off as the waveform goes negative. Only conducting as it goes one direction and blocks the other way. So as the waveform is summed together, you get a waveform at twice the 60hz cycle (120hz) and the waveform only goes positive and back to zero volt line instead of the above and below as comes out of the transformer.
The big deal is the turn on and off of the diode. The situation is complicated badly by the fact that the capacitor that follows presents a heavy suck to pull current needed to top it off and the impedance varies during the cycle. The current pull waveform is highly distorted and is spiky and nasty! Metering voltage reveals little about what's going on with the current at that point. If I had time, I'd dig up some waveforms and the pictures tell this story much better than my words.
This current pull nasties carry on to some lessening degree into and even through the power supply depending on many factors. The wire size, quality of connections and all the impedances involved between the elements. Where and how good grounds are done make big differences.
Another thing...those sharp spikes of current make high frequency waveforms and this can result in
radiated energy around the diodes too. So the way diodes turn on and off can wind up effecting the radiated energy
and the resulting power flow. There are a number of different diode designs and some level of differences can be observed in the audio that comes from modulating these supplies with the audio that we much want to come through so perfectly.
To turn to real life stories to relate the rubber meets the road part of this...
I've heard different brands of same model tube rectifiers sound different switching them in the same amp!
I have the several of the same basic amp, EL84 amps btw, that have variations in a few things but one of the big ones is tube rectifier versus SS. Tubes always have that tube ease of presentation!
I have a friend that spent much time and money on investigating sonic differences in (ta-da!!!) rectifier diodes in a tube preamp! He socketed the rectifier stage so different ones could be dropped in pretty quickly. He tried different specific styles of diodes and also different configurations all the way up to and including hybrid tube and SS full wave bridges. After much time on this project, he came away with favorites, but certainly the overiding story is they all are somewhat different.
You can spend higher dollars on some of them and others not so much. But fast and soft turn on\off is worth doing most certainly. Simply less of the traditional solid state hardness and more liquid naturalness to put it simply.
Better than ordinary rectifier...
http://parts.digikey.com/1/parts/1068071-diode-ultra-fast-4a-1kv-do-201ad-mur4100eg.htmlPretty good diode...
http://parts.digikey.com/1/parts/415556-diode-fred-1000v-12a-220ac-dsei12-10a.htmlAnd a really good one...
http://www.partsconnexion.com/product7564.htmlHope you can follow the story line and how this simple change can matter in your amp!
Mark
Fri Feb 03, 2012 4:57 pm 
