Tube vs. Solid State Rectifier

There's lots of talk among gear enthusiasts about the differences between amps with solid-state and tube rectifiers. Some players prefer one or the other or even claim one is better than the other. So what is the big deal anyway? In this article I will briefly enumerate the differences between the two.

What is a rectifier?

The whole subject of tube vs. solid-state rectification begs the question: what is a rectifier anyway? A rectifier is a device that changes alternating current (AC) into direct current (DC). The power in all wall sockets is AC but all amp s operate on DC so a rectifier is required for operation. It is important to note that the rectifier is not in the signal path of an amplifier but rather the power supply. 

Tube Rectifiers

 All early tube amps used tube rectifiers because solid state reciter had not been invented yet. Yet even after solid-state rectifiers became more common place some manufacturers stuck with tubes because early solid state devices were expensive. Today most new designs have solid state rectifiers.  

Tube rectifiers are inherently imperfect. They have a voltage drop across them and internal impedance. Lastly you cannot use lots of power filtering with a tube rectifier. So what does that mean for sound? The internal impedance of a tube rectifier means that when the amp calls for current (say when you strike a note) there is a slight delay in the delivery of the current and a slight drop in voltage. This is known as "Sag". This leads to a singing sustain and touch sensitivity. The drawback is that is makes the bass response of an amp softer. This effect is compounded by the necessary use of less power filtering which also cause softer bass response.

Tube rectifiers have voltage drop across them.  In typical tubes used in guitar amps 25 to 50 DCV are dropped.  This drop in voltage can lead to some tonal change with lower voltages being a little browner sounding breaking up little sooner. 

In many amps tube some common tube rectifier types are interchangeable but you must be careful since some type draw more heater current and in the bias must be adjusted in a fixed bias amp. 

Solid-state Rectifiers

After the 1950's more and more amps were built with a solid-state rectifier. Today the majority of tube amps use solid-state rectifiers. Probably the bigger driver of the change was cost. Solid-state rectifiers cost a few cents, do not require a filament winding on a transformer to run the tube, and rarely have service issues. The solid-state rectifier works more perfectly from an engineering stand point. The delivery of the current is quick and you can use whatever amount of power filtering you prefer. The drawback is that you do not have sag which can be a real bummer for some folks. Solid-state rectified amps sound tighter and punchier that their tube counterparts. It should be noted it is very easy to build sag into solid state rectifier and make it behave like a tube or even have switchable tube and solid-state sounds.  While is inexpensive to do so very few manufacturers do this. 


So which one do I want?

Both are good for different sounds. In general players who play cleaner styles or are looking for some compression get along well with tube rectifiers. Blues players love them for their singing quality and touch sensitivity. If you are going to be playing heavier music like metal or hard rock solid-state is the way to go. Of course their are many exceptions. I think a player would benefit from having amps with both types or better yet amp that can do both sounds-- it's like more paints for an artist.