What's the greatest bargain in SET these days?

A summary From Pro Guitar: What is a Rectifier?

What does a rectifier do? If you don’t know, don’t feel bad, you’re about to find out. A rectifier changes alternating current (AC), like a wall outlet, to direct current (DC) that is required to run all electronics inside your amplifier. That’s it, it’s really that simple. The AC voltage comes from the wall into the transformer of your amp where it is then run through the rectifier to get DC voltage. This is before all audio circuitry so an important thing to realize is that NO AUDIO SIGNAL PASSES THROUGH THE RECTIFIER. It is purely for voltage conversion. So how does it affect the tone if no audio passes through it?

Rectifier Types:

So now we know what the rectifier does. In audio, guitar and bass tube amplifiers, there are two different types of rectifiers you will see, solid state and tube. There are several commonly used tube rectifiers in amps, 5U4, 5AR4 (GZ34), 5Y3, and 6CA4 (EZ81). Each has different voltage handling and characteristics for different output levels and circuits but each accomplishes the same task in the circuit. That’s it, no magic, no mystery, purely a power issue.

A solid state rectifier is made up of two to four diodes in a circuit (generally, there are single diode rectifiers but they are somewhat uncommon in guitar amps) or an IC that is made up of diodes. The solid state rectifier, while being diodes and not tubes, accomplishes the same task as a tube rectifier, it is simply there to convert AC voltage to DC voltage.

Tone:

So if a rectifier does not pass audio, how can it affect the tone of an amplifier? Well, the rectifier is the first post-transformer link in the power supply and changing the power supply voltage will cause different tonal characteristics. Tube rectifiers have an internal resistance so the more current that is pulled through a tube rectifier, the more the voltage drops which in turn causes the output power of the amp to drop. This drop affects the rise time of the tube (the time taken to produce the proper voltage output) and as the note decays the voltage builds causing a compression like effect. This is commonly referred to as “sag”. Since low frequencies require more current to reproduce, this sag causes a tube rectified amp to have a spongier low end and distort easier. This natural compression and sustain is sought after by many guitarists of certain genres (blues, classic rock, country) but not for everyone. Many players feel that a tube rectified amp responds better to touch dynamics and sound warmer than the solid state counter-parts. Different types of rectifier tubes will have different tonal characteristics in the same circuit as well but, as with all tube substitutions, BE CAREFUL. Not all rectifier tubes are interchangeable so consult a qualified technician before substituting.

Thanks for that but I am wondering what the specific noticeable effect to the sound is for this amp specifically by changing the rectifier tube as suggested.

I'm very much in to TONE. The tone of an audio amp for me is extremely important. Therefor, the right rectifier makes a world of difference in the total sound.

Mapman,
Warmer, smoother, tone of instruments accurate, well saturated color, and so forth...

Ok, I did not explain that too well. Let me try again: in music, the timbre also known as tone color or tone quality is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the perception of timbre include spectrum and envelope.

In simple terms, timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness. For instance, it is the difference between a guitar and a piano playing the same note at the same loudness. Experienced musicians are able to distinguish between different instruments based on their varied timbres, even if those instruments are playing notes at the same pitch and loudness. (This with a little help from the Wikipedia).

The little Dynamo does all this and more in spades.