Short Guide to
Rectifiers

When searching for a new amp you may have heard the word rectifier come up, particularly with Mesa Boogie's Rectifier series.

In actual fact, every tube amp needs a rectifier; but what are they and how does it affect the sound of your amp... Time to find out!

Introduction

One of the things you may have seen when hunting for an amp is the mention of a component called the ‘rectifier’. Sadly it is not as cool as the name suggests but is a vital part of making an amplifier work.

It does not sit anywhere even close to the tone section and your guitar’s signal doesn’t run through it but it still plays a big part of the tone. A lot of the reason people love old Fender Twins and classic 40’s, 50’s and 60’s amps is that a lot of them still used tube rectifiers.

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So what is a rectifier?

Glad you asked. A rectifier changes the AC current coming from the power outlet in the wall to DC power that works with modern electronic components. This is handled by a device called a diode which in most modern amps is made out of silicon and is what we would refer to as solid state technology.

Before silicon and modern diodes came around in the 1950’s everything used a valve rectifier. These are just like the other valves you will find in your amplifier just with different ratings and fittings. There are a variety of different options available that would be chosen depending on the amount of power created by the power amp valves.

There are still amps that use valve rectifiers today and even some that let you choose between solid state and valve. The king of which has to be the Mesa Boogie Rectifier range of amps where the Dual and Triple rectifiers have a switch on the back to go between both options.

So what is better?

Right, this is where things get tricky to explain. The big difference in tone is that the silicon chips are miles better at working as a rectifier when compared to variable and fragile tubes. A silicon chip can provide the perfect amount of power through the entire system without failure as long as it is getting the right AC current from the wall.

This means you will get the same amount of power running through the amp no matter what changes you make. This is great for stability because as long as you have decent, clean power your amp should sound the same every single night.

A tube rectifier is a lot more fragile, they break easily and wear down over time. Plus they aren’t even really that good as rectifiers. In some amps they work perfectly, but when you four 6L6 power amp tubes running extremely hot the rectifier tube will not be stable and will affect the sound of the amplifier.

Solid state is better right? Why do some amps still have tube rectifiers?

Not at all. In fact, many will argue that the imperfect valve rectifier adds so much to the sound when running hot that it is worth the inconsistency.

For some the silicon circuit is too perfect and lacks a lot of the flavour and texture that comes from a valve rectifier.

I thought it wasn’t in the tone section, how does it affect the sound?

So when you have a silicon rectifier it can easily supply the correct amount of power at any time to make sure you get what they have defined as the perfect tone.

A valve rectifier can never provide the perfect amount of power and when pushed too hard you will start to get the effect known as tube sag as it can’t provide what the power amp valves need to run properly.

What is sag?

Sag is when the valves can’t perform properly due to being run too hot with odd voltage from the rectifier.

This creates the effect of a slower attack with a much smoother higher end. Think about it like a compressor that dulls the attack and gets rid of a lot of the harsh high end that you would get before the sag kicks in.

If you listen to a lot of blues or rock players, when they go into a mid gain solo that just seems to glide forever, part of that will be an overworked tube rectifier smoothing out the tone.

Different rectifier tubes will drastically change the amount of sag. For example smaller amps commonly come with a 5Y3 Rectifier which is going to compress the sound the most and give you that vintage sustain at lower volumes. On the other hands things like the GZ34 or 5AR4 don’t start to sag until they are hit really hard (one of the reasons vintage high power valve amps sound best when cracked up to max).

So what do you want in your amp?

Depends on the sound you are after. The best idea is to come to a shop like Andertons and try a range of different amps that use valve and solid state rectifiers. Or try something like the Mesa Boogie Dual Rectifier that has switchable valve and solid state rectifier modes so you can hear the difference on the same preamp and power amp.

Generally, heavier players will want a solid state rectifier for its excellent efficiency and response meaning you can get those really tight rhythms night after night.

Players who want to mostly focus on blues, rock, jazz, pop may want to look at a valve rectifier for that sweet sustain and beautifully compressed tone it gives you (when provided with the right power)

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