The job of the rectifier is to convert alternating current (AC), which is received from the wall socket into the power transformer, into direct current. Direct current (DC) is needed to operate all of the circuitry in a guitar amplifier. This process takes place through a device called a diode. Diodes act like a one-way valve, allowing current to flow in one direction only.
Today’s diodes are made out of silicon.
The tube diode was the first diode ever invented (in fact it was the first tube ever invented). For many years it worked quite dependably and it was the only choice for rectifying current for high voltage power supplies. When solid state technology was developed in the 1950’s, it was found that solid state diodes could do the job of tube diodes, only better.
A tube rectifier has internal resistance. The more current that travels through a tube rectifier, the more the voltage drops. When the voltage drops, the power of the amplifier also drops. The tube rectifier has the drawback of not being able to provide a consistent voltage when it’s under load. The other drawback is that the tubes themselves run hot, and can be relatively short-lived. Unfortunately, modern day sources for rectifier tubes are not very reliable and, even in their prime, these tubes were usually the weak link in most amplifiers.
An amp with a tube rectifier tends to sound much spongier in the bottom end. Low frequency notes take more current through the power tubes to reproduce. This increased current causes a voltage drop in the rectifier tube and the amp loses power. So, when more power is actually needed, the amp gives less. Because of this, a tube rectifier amp will sound spongy and more distorted at high volumes. This, probably more than anything, is what gives a vintage amp its sound and color.
A solid state rectifier has no internal resistance whatsoever. It has a very consistent fixed voltage drop that occurs both at zero or full current (approximately .7 volts). When an amplifier needs power at low frequencies, there will be no limit to the current that travels through the rectifier. This results in an amp with more headroom that is punchier, more articulate and able to deliver the goods in the bottom end.
In my opinion, all amps should have solid state rectifiers. I don’t believe there are any really good rectifier tubes on today’s market and, even if there were, why use them? The technology is obsolete; they are horribly inefficient, and far more expensive and troublesome to build into an amp. These tubes, no matter how good, will routinely need replacing, adding to your maintenance expenses. Besides that, tube rectifiers kill the headroom of an amplifier. If you want that spongy, vintage sound, there are other ways to do it. I have successfully designed and built amps that have replicated that soggy bottom, vintage tube rectifier sound using solid state rectifiers and various circuit modifications.
Of course, if you have a vintage amp that uses a tube rectifier, by all means keep it that way! That’s what makes it sound the way it does. But if you’re contemplating getting a new amp, I recommend avoiding future headaches by staying away from tube rectifiers.