Tube Basics 101: What is a rectifier tube for?

In laymans terms please:

What is the function of a Rectifier tube (such as the 5AR4/GZ34 found in my tube preamp)?

Why/How would the Rectifier tube affect the sound created?

How would this differ from the function of a typtical Driver tube (such as a 6SN7, 12AX7, 12AU7)? Also, would a driver tube typically have more affect on the overall sound (i.e. Which tubes would you roll out first if you wanted to change the sound of your preamp?)

Also, what is a "Getter" tube?
A rectifier is a diode that converts AC to DC. Since every portion of a typical linear power supply in a vacuum tube amplifier is coupled (in part) to the output, changes in any component in a power supply can often radically effect the resultant sound - rectifier tubes, power transformers, resistors, capacitors, and inductors all can and do effect the sound.

The getter is not a tube, but rather a portion thereof. The getter is a metal element within the envelope coated with a substance which reacts with excess gasses trapped in the tube as the vacuum seal is applied. The getter both aids and maintains the vacuum within the tube, however it has no electrical function per se.

To explain with any more breadth requires at least an elementary knowledge of the topic. In other words, it is difficult to explain what a diode is without referencing other basic electronic terms and concepts. If you are interested in further exploration, several excellent online tutorials exist regarding basic electronics.
The rectifier tube is used to create a direct current from the alternating current of the incoming A/C power. The rectifier tube is a diode. That is it transmits the current only in one direction. The plate and cathode charges are responsible for the allowing of current in one direction only. The resultant sine wave of the A/C source is just chopped off on the negative side of the cycling waveform. So the power becomes direct current, but it still is going from zero to full back to zero just as the peak of the alternating current did, with a gap of staying zero when the negative AC part of the current is being blocked.
The negative portion can also be 'rectified' AND inverted to turn the negative side of the power pulse into the positive side. This is called a "full wave" rectifier. The resultant waveform still has the sine wave shape of pulses, just all positve, from zero to full and back to zero, (with no gaps) all in the same polarity, thus Direct current.(cycling from zero to full to zero constantly, but always positive)
For power supply that deliver a positive DC voltage from ground, AND an equal negative DC voltage (usually for balanced operation) the power supply is doubled up and one full wave rectifier does the positive, another the negative rail.
(the reason for DC smoothing capacitors is to smooth out these pulses and offer a steady direct current.)
So those giant caps in your amp serve more than just one purpose. They store energy yes, but they also smooth out the pulsing of the power supply.
The rectifier tube is not the direct cause of the quality of the sound in the power supply. The whole design of the power supply is what affects the sound quality. i personally would say as long as the rectifier tube is working properly, that is all it can do. A 'quality' tube may be better because it actually does the job better.
The difference between a power supply tube and a signal tube is that the power supply tube is a 'rectifier',(a diode) it does NOT have a direct connection to the signal. The Driver tube DOES carry and amplify the audio signal. And the quality of the driver tube is very important to the quality of the final audio signal.
Different designs use tubes in different ways. Some use both sides of the tube as the stereo, some use only one side. all sorts of possibilites. But no matter how it is designed, the tubes that carry the signal are the important ones.
In many tube circuits a second tube is used called a 'cathode follower' This tube (or tubes) are not as important as the driver tubes. They can be of a lower quality and have less impact on the sound.
(For example my VAC has 2 driver tubes 12Ax7 and two cathode follower tubes 12au7.
So for my preamp the 12ax7 should be the best i can buy for best sound. but the cathod follower the 12au7 only need to be decent.
So find out which tubes in YOUR preamp are driver tubes and replace those with better quality tubes. You can leave all the others as is.
Elizabeth must have stayed at a Holiday-In Express.
No, I call it being helpful instead of being a (*) like you.
*(fill in the blank with whatever insult gives you the biggest laugh)
I apoligize if my humor affened you Elizabeth. It wont happen again.

"Affended"? Have a dick-tionary the next time you apologize.
Thanks Palasr and Elizabeth. Thats exactly the sort of information I'm looking for.

Trying to decide which tubes to replace in my preamp and which will give me the biggest bang for the buck. Lot of people wax poetic about the sound quality from swapping rectifier tubes, but I was also gathering that in practical terms the difference in sound from these tubes is less significant. I appreciate your no-nonsense info Elizabeth.

As far as the other tubes in my particular preamp, the (2) 6SN7 are both listed as drivers for the line stage. For the phono stage I'm a little less certain. I dont know which is the driver or even if one is a cathode follower. I may have to contact the manufacturer to find out.

Since you might be able to help, the preamp is the new Modwright LS100:

Here is a little blurb from the designer as it appeared in a review on Perhaps this would help determine which tubes are drivers/cathode followers:

"About the 6SN7 double triodes, we use just one half per channel. This gives the advantage of extended tube life as you can channel swap the tubes to use the other two halves. Theoretically we could have used a single 6SN7. In the case of our phono board, we do use a single 12AU7 and 12AX7 for two gain stages, again half a tube each per side."

You hit the nail on the head in that I really want to know which tubes will affect the sound more, and therefore which tubes to swap out first. Of course, my next question is going to be which tubes I should replace them with? NOS or current stock?
Kick a man while he's down.

Here is a link you may find informative....
A taste of tubes

Thank you for the reference. I never saw that wonderful article. Clever and informative. Thanks!
They use one 12au7 because it is a not too important cathod follower. The two 12ax7s are the audio tubes.
So get good 6EH7EH (Electro harmonix brand) or Tung Sol 6SN7GTB and get the matched so they are matched one left/ one right then the other two sides matched. (Sylvania are the NOS 6SN7WGTA to buy but cost is three times the others I mentioned.)
So say a 72/68 and another tube that is 67/72 for and example. If they are better matched so both sides are the same, they will cost more.
Same goes for the 12ax7s. (RCA)
When you can swap the sides and double the life that is cool.
I would swap the sides on a regular basis, like every three months/or six months if it is not to hard to do.
I disagree.

CF is very important in the circuit of the topology you described! Try bypassing the CF (without replacing it with a transformer)in your preamp's output circuit and you will see how important it is on how the preamp will sound and how it will perform driving the load.

Just my opinion....
Isn't that like saying any average steering wheel will operate a car, but take it out and let's see how well the car operates?

Actually, the preamp Phono board uses only (1) 12AU7 and (1) 12AX7. I see how you thought it was (2) 12AX7s from the quote I inserted, but if you re-read it again you will see. Also, I double checked on the Modwright website that I linkd in my post above to be sure.

So given that, I'm still not sure if either/or (12AU7 and 12AX7)are cathode followers, as you say. Do you still think so? Does this change any recommendations for tubes to change?

Thanks everyone for all the info. I'll check out that article and probably have some more questions.
The au is a cathode follower. The ax is using both sides of the tube and the two sides should be well matched and very 'low noise' quality.
The 12AX7 is the 'most' important tube IF you use the phono section regularly.
In response to the preamp question, I have had great success in swapping out the 12au7, for NOS RCA cleartop 12au7's.
Hi, I would suggest that you call Andy at "Vintage Tube Services" and tell him what model pre you have and he will help you with selection and sell you tubes that are quite and won't break the bank.
Good luck, Tish
Elizabeth (or anyone)-

Is it safe to assume then that a 12au7 tube is always a cathode follower?

And if I can reiterate or summarize a bit:

Sounds like the 12au7 and 6sn7 driver tubes are most important to the sound and should be swapped out first if trying to upgrade the sound in some way. The 12au7, being a cathode follower tube - some say it is important as well, some say not as much affect to the sound. Same goes for the rectifier 5AR4 tube - some insist you should swap them out for better sound, some say it's not so important. But in any case the cathode follower and rectifier would not be the top choices for tube rolling until trying the others first.

Do I have this about right?
A power supply's rectifier(and it's quality) is VERY important to the sound of any amplifying circuit(phono, mic, preamp, power amp, etc). Anyone that has taken the time to install, say a Mullard Blackburn GZ34/5AR4, in the place of most other tube rectifiers(of the same family), or Fast/Soft Recovery Epitaxial Diodes, in the place of standard SS rectifiers, will likely attest to the improvements of presentation(across the board). Generally speaking; the sound will open up, have greater dynamics and a smoother(less grainy) high end. What you are listening to, through your speakers IS(in actuality) your house current, as prepared by your power supply. Your speakers are connected to your power supply, through your output devices(tubed or SS), and the DC output of said power supply is modulated(YES- the correct term) by those devices(basically switches), as directed by the musical signal. Is that the WHOLE story? NO! Every gain stage is important. Phase splitters and driver tubes BOTH contribute tremendously to one's final sound. BUT- to ignore the importance of the power supply's rectifiers, is to rob yourself of MUCH musical pleasure. I didn't stay at a Holiday Inn, but I have been modding audio equipment, and pro gear, for over 30 years and have made many a discerning ear happy, in that time.
I appreciate that, in the end, every tube in the circuit will matter to the sound and performance. I was fully expecting that reponse.

I just wanted to get some sort of consensus as to which tubes would have more bearing on the sound/performance - driver, rectifier, cathode follower, others?. So if you were wanting to change tubes one at a time and hoping to enhance sound/performance, in which order would you change them?

Drivers - Rectifier - Cathode Follower?
Drivers - Cathode Follower - Rectifier?

Also, I have to assume that, like everything else, eventually the law of diminishing returns comes into play. Not everyone's ears or systems are designed to be able to discern the differences between every single cable or interconnect that you insert here and there. I fully expect that the same is going to be true of tubes.

I'm completly new to tubes. I just want to approach things from a logical standpoint and roll out the tubes one at a time starting with the ones most likely to alter the sound. At some point I might say, "Thats good enough" or maybe I wont even be able to discern any differences.

Phono driver tube (if you use phono stage much) then main driver tubes, (then phono cathode follower,if use phono) then rectifier tube. finally main Cathode follower IMO.
Like pwer cords and interconnects, folks will ague this endlessly if it is thier 'thing'.
After the main audio tubes it really is not a big deal..
Thanks again for the basic no-nonsense info.

It appears the my preamp has no main cathode follower. The only tubes in it are the ones I mentioned: (2) 6SN7 drivers for the main, (1) 12AX7 and (1) 12AU7 for the phono and the (1) 5AR4/GZ34 rectifier.

I suspect the preamp I am talking about (once again, the Modwright LS100) is more of a 'hybrid'design than a true tube preamp, but I dont know the distinctions exactly. In any case, there doesnt appear to be a cathode follower - dont know if that seems strange to any of you?

Also, I wonder what all of your opinions are about something I was reading in another thread here on Audiogon. There was a link to another article (Joe's Tube Lore - where the author basically said that there are no 12ax7 tubes that are all that good. The author suggested that anyone interested in getting better sound should replace the 12ax7 tubes with 5751 tubes, which are, for the most part, interchangeable with the 12ax7.

Is this something that is a given or fairly common knowledge? Would you agree with this assessment? And also, if you do replace 12ax7 tubes with 5751 tubes, can you still use the 12au7 cathode follower, or do you need to replace those with something different as well?

Thanks again everyone!
Hello Mr N- While it is certainly true that everyones' aural accuity, and system resolutions vary; tubes in circuit make a dramatic difference, and one must be nearly deaf to miss their impact. Since you mentioned the 6SN7 family, I'll start there, as the driver will have an effect on ALL your inputs. This tube: ( is an excellent performer, that won't break the bank(like my faves; the TungSol round plates, and Sylvania 6SN7W, tall bottles). They are easy to find(right now anyway). Whatever you buy; be certain the triodes are balanced, and the pair also(if more than one is used in that stage). When you replace the phono tubes; once more, balance is important, but also- get CERTIFIED LOW NOISE tubes, as the gain there is much higher, and any noise will be amplified( After you've gotten accustomed to the new flavor of your system; find a NOS Mullard(Blackburn Plant) GZ34(, and enjoy! OH, BTW: The Mullard rectifier will probably outlast you, and your preamp. Here is a site that will give you an idea of what presentation to expect from some of the difference NOS tubes in the 6SN7 family. I've tried all the top contenders listed, and can vouch for the veracity of the opinions given(
While it is certainly true that everyones' aural accuity, and system resolutions vary; tubes in circuit make a dramatic difference, and one must be nearly deaf to miss their impact.

Well, again, I am pretty new to tubes, so I cant say that that couldn't be the case.

When you replace the phono tubes; once more, balance is important, but also- get CERTIFIED LOW NOISE tubes, as the gain there is much higher, and any noise will be amplified

But my preamp has only one driver tube in the phono - a single 12ax7, so I dont know how to take what you are saying. Match it to what? Should it be matched to the 12au7 follower?

And thanks for the specific recommendations. Will definitely consider some of these. Hoping for more recommendations as well.

On a side note, others have told me the new stock Shuguang Black Treasure 6SN7/CV181-Z are good tubes to use. This is not to bring up the NOS vs current stock debate. But I wouldnt mind having one or 2 recommendations from both (NOS and current options) for each of the tubes in my circuit.
I based my comment on what you said about having a 12AX7 and 12AU7 in the phono circuit. Both are, "dual triode" tubes, and(as you have one each for both channels), if the two triodes(WITHIN EACH TUBE) are not balanced, neither will the sound be, from that stage of your system. Of course: that will bother some, more than others. Did you look at the Upscale Audio page, on grading tubes? The better the grade, the closer the triode balance(from most sellers). Personally- I've never heard a Chinese tube that I wanted to listen to again. But- who am I to say what's right in someone else's listening room? Happy listening!
Just went through this situtation myself! Brent jessee helped a great deal! Up graded to siemans 12at7 tubes from rca's- huge improvement! Than upgraded rec.and what it did was increase presence,depth,sound stage and gave a punch to the low end!it has to do with the rec. Is an important part as to providing higher current to the pre. I liken it to the right pre and amp combination. Each sys is going to react diff.its trial and error.try diff. Rec. And see which one you like the best!this (to me )
falls into
More or less tweeking your sys. Assumeing pre,amp,and speakers work well together.brent explaint it better, but it still comes down to "what you like
I went thru 6 diff. Amps,7 pre's and 15 pair of speakers untill I hit on the present combo. And it was worth it!!the tubes power and rec. (Fine tuned) the sys. To exactly what I was looking (or listening for).Brent jessee was a great help, can't recommend him highly enough!
I have question , will a rectifier tube affect the volume ? The left channel of my tube amp sounds a bit louder than the right channel , i was hoping that a rectifier could even out the sound in both channels , i have swap  the 6SN7, as well as the 2A3 tubes , the result is the same , any thoughts ? , i have bought a new and expensive volume potentiometer (100 K)to replace the one it has (50 K ),  will solve this issue ? , many thanks !!!

hi ibuy,
it is hard to determine the exact cause. it could maybe any of the resistor in your preamp that has drifted in value. it would be best to send it back to manufacturer to check out. However, if the imbalance is near the lower volume settings then it is definitely the potentiometer problem, because generally potentiomenter are poor in channel balance at lower volume setting unless you purchase those costly potentiometer.
Hi, Phillip , thanks for your response , my amp its totally new , unhappy with the Capacitors it came with i bought the best brand i could find , "Jensen" i changed three of them , , the amp its beautifully made Point to point and is starting to sound much to my liking , i just changed the RCA  5R4WGB rectifier with another one , can't tell which brand is it as the lettering its almost gone , BUT it made a difference in sound , i think both channels play more balanced , your are right about the potentiometer , it does play unbalanced at lower volume , which indicates that the issue is the potentiometer . fortunately i have one made especially for AN , by Audio Note , thanks again !!!