Tube Vs. Solid State Rectifiers

Written by
Logan Tabor
Published on
January 22, 2021 10:36:59 AM PST January 22, 2021 10:36:59 AM PSTnd, January 22, 2021 10:36:59 AM PST
It is generally believed, in the world of guitar amps, that any products whose descriptions contain the words ‘solid state’ will ultimately be inferior to those who contain the word ‘tube.’  And while there is no doubt that the tube amplifier is a beautiful thing which has withstood the tests of both time and technology, many of us seem to make big buying decisions based solely upon whether or not an amp is ‘tube’ or ‘solid state’ rectified.  So much to the point that amp manufacturers have based entire product lines and marketing campaigns around the word ‘rectifier.’ But what is a rectifier? What is a rectifier’s job inside our guitar amps? And is tube really better than solid state? Today we aim to address all of these questions, and to give a side by side comparison of tube vs. solid state rectification by replacing the rectifier tubes in a number of well-known amps with Mojotone’s Solid State Rectifier.

 

What Does A Rectifier Do?  
In simplest terms, a rectifier is what converts AC power into DC power.  Power will enter an amplifier from the wall plug in AC voltage, it will then work its way through the amp’s power transformer, and eventually to the rectifier where it’s converted to DC voltage.  This is necessary because the rest of the guitar amp’s circuitry requires DC voltage to operate.  
To be even more specific, a rectifier is simply a diode (whether tube or solid state).  And a diode is a small ‘valve’ or ‘gateway’ that forces electricity to flow in only one direction.  In guitar amps, this process typically also involves the voltage being bumped up to the amount demanded by the other tubes in the circuit.  In the USA for instance, power comes from the wall and into the amp at 120VAC. The power transformer will then bump the power up to around 330VAC.  Finally, the rectifier will convert the power from AC to DC and often bump the voltage up to around or above 400VDC.  
The rectifier itself is not actually in the amplifier’s signal chain, meaning your guitar’s signal does not pass through the rectifier at any point.  So what’s this big debate over solid state vs. tube rectifiers? If the guitar signal doesn’t even pass through this part of the amp, how could it even affect the amp’s tone?  

Tube Rectifiers
To reiterate, a rectifier (whether tube or solid state) is simply a diode.  The tube diode was the very first diode ever invented; this was also the very first vacuum tube ever invented.  And while it is true that tube rectifiers and solid state rectifiers both perform the same task, it is also true that the amount of DC these different devices can make and the speed at which they can do so, is very different.  This is actually the biggest part of why many players live by the idea that tube rectifiers are superior to solid state rectifiers (sonically speaking). You see, tube rectifiers are essentially slower at converting AC to DC. When an amp is being pushed and a player is hitting big chords, a lot is demanded in regards to rectified current.  The tube rectifier can’t keep up with demand as well as the solid state rectifier, and when this happens the tube rectifier experiences a voltage drop for a few milliseconds while it catches back up. To the ears, this is what we refer to as “sag.” Sag is really what gives players the classic compression that defines the traditional tube amplifier sound.  When sag is heard (and felt), players often start to use words like “bloom,” and “spongy,” to describe the sound and playing feel. Many amps have become famous from this sound; Fender’s Deluxe Reverb and Super Reverb, the Marshall JTM 45, Vox AC30, etc.  
Sag isn’t only determined by whether or not an amp utilizes a tube rectifier or solid state rectifier, however.  Different tube-rectified amps have different voltage requirements, and thus use different values of tube rectifiers.  The 5Y3 rectifier tube, used in a Fender Tweed Deluxe, is a small rectifier tube that produces less DC voltage and thus exhibits more sag/compression.  Heavier-duty tube rectifiers include the GZ34 (5AR4) and the 5U4G; these tend to have a quicker response and supply more voltage which means they will exhibit a tighter sound with less sag.

Solid State Rectifiers
Solid state technology came about in the 50s -- in the case of rectifiers, it was in the form of a small silicon diode.  These quickly became less expensive than tube rectifiers and were thus used more often. They also have no internal compression, and are said to work more ‘perfectly’ in the world of engineering.  Solid state rectifiers have much less, if any, voltage drop and can deliver more current more quickly (which is why they are used in higher wattage amplifiers, where tube rectifiers are rarely seen in amps over 40 Watts).  
Sonically, this yields a tighter sound with much less sag.  A more solid low end with lots of headroom is typical (which is great for metal players/fast pickers).  The drawback here is obviously that with little to no sag, many players miss that vintage compression and spongy playing feel.  Preamp and power tubes will also exhibit some sag of their own when hit hard enough, so even solid state-rectified amps containing preamp and power tubes will have some sag if pushed pretty hard, but it will typically not be to the extent of a tube-rectified amplifier.  
Here again, many famous and popular amps were designed to use a good solid state rectifier: Fender Twin Reverb, Carr Rambler, etc.  Even Mesa Boogie’s ever-revered Dual Rectifier allows the user to switch between tube and solid state rectifiers.  

So Which Is Better?
Like with many aspects of personal guitar rigs, this all has to do with taste.  Some players will require the tight and quick response of solid state rectifiers, where other players want the heavy sag and blooming compression of a tube rectifier.  There is no right or wrong answer here. It is always best to take your primary guitar into a shop and play as many amps, first hand, as possible. You might be shocked to learn that out of five amps, your three favorites all contained a solid state rectifier.  Who knows!?

Let’s Compare...
One important thing to note is this: While on rare occasion, some tube-rectified amps do allow for the use of different types/values of rectifier tubes, please be aware this is not typical practice.  If you are looking to experiment with different values of rectifier tubes, it is best to contact the amp’s manufacturer or a certified technician prior to making this kind of change.  
For today’s experiment, we will actually be replacing the rectifier TUBES in three fairly well-known amps with this Solid State Rectifier from Mojotone.  I’m really curious to hear the difference these guys make. They are plug-and-play, so no further adjustments will be required here; I’m just going to carefully wiggle my rectifier tube out of its socket and replace it with the solid state rectifier (see video below).
I’m expecting this to give me less sag at higher volumes on all of the amps, and I’m really interested to find out if I enjoy this new responsiveness.  I am also expecting this change to be subtle at best, but isn’t that what all of this tweaking is about? Alright here goes nothing…



TWEED DELUXE


I found that the Tweed Deluxe (which was using a 5Y3 rectifier tube) showed a marked difference when I inserted the Solid State Rectifier.  I always love this amp, but I think I actually enjoyed it more with the SS rectifier plug implemented; it had less sag and a strong immediate attack which sounded great to my ears.  


GA5


This was interesting as I found that the GA5 did not necessarily exhibit less sag with the SS rectifier plug inserted.  In fact, at certain times I felt like the SS plug had a little more sag, or at least a more dramatically squishy playing feel.  This could potentially be attributed to the sag of the preamp and power tubes rather than the sag of the rectifier itself.  


Deluxe Reverb


This was the only amp utilizing a GZ34 in the rectifier tube socket.  With that in mind, I actually heard the least amount of change here, which makes sense considering the GZ34 is capable of supplying more voltage more quickly than a 5Y3 rectifier tube.  While I did notice some change in attack and clarity here, the difference was minimal.