Tube Basics 101: What is a rectifier tube for?

Elizabeth-

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.

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?

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: http://www.modwright.com/products/17

Here is a little blurb from the designer as it appeared in a review on 6moons.com. 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?

Rodman99999-
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?
or
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.

Thanks!

Elizabeth-
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 - http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html) 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!

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.