Tubes for a pre stage... matched NEW or unmatched identical NOS?

Certainly all tubes are subject to system matching. My amp tends to run a little laid back, so the extra detail from the clear tops was welcome. Yes my Amperex and Philips tubes best the clear tops…..but now we’re into $200 to $600 for a pair of tubes, and not $40

Another surprise, early to mid 80s 6N23P Russian tubes (Rocket logo)

I'm curious if the clear tops were a cost saving measure? Definitely simpler construction.

Perhaps a thinner glass.

Anyone run them for 24 hours on heater only before listening?

i agree that clear tops can be a little tizzy... regular top getter rca’s seem a touch smoother

as usual, tubes, like anything else in a good system, is subject to synergies (or lack thereof) and the taste of the listener

You guys like the cleartops??

Couldn't get them out of my pre fast enough. Way too bright in my system.

Brent also carries a large selection of rare rectifier and power tubes.

I think many of you know that Brent Jessee is one of the most reputable providers of NOS tubes out there. He will have one of the largest selections, and the tubes go through a rigorous testing before being sold.....and he warrants all of his tubes for 30 days, and many for up to 2 years (not sure of the difference)

This link will take you to the best page I have ever seen on 6DJ8/12AU7/6922/7308/ECC88/E88CC/CCA/6N23P(Russian)/etc. He explains the difference in tube suppliers and their country of origin, and what to expect sound wise from each version of the tube, even how to translate date codes to date your tubes. NOTE: He focuses mostly on Euro tubes, with some information on American and Japanese tubes as well. It's a long read, but should definitely be bookmarked and printed out for future reference....especially for tube rollers.

http://www.audiotubes.com/6dj8.htm

Just dropped (2) RCA 12au7 "Clear Tops" in my Line Magnetic DAC. Pleasantly surprised - they are terrific so,... I agree with the hype 

Agree with  @vthokie83 RCA Clear Tops are a fantastic tube at an amazing price.  Way better than any new production that I have tried

$30 new production tubes, or $20 RCA Clear Tops…..no comparison 

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets 

The problem is what is 'well matched'? At the datasheet params? NONE of my tubes operate anywhere near them.

I've bought plenty of NOS 'matched' 12AU7 & commercial variants. NOT one came close to the claimed Gm when operated at the amplifier parameters. NOR were the Gm matched at datasheet parameters. 

NOS tubes often have significant gas after ½c. on the shelf and need a while for the getter to clear it. Some advocate baking, but others say never. Induction heating may be the answer.

Expect any NOS tube to change significantly over the first number of hours.

Methinks Confirmation Bias accounts for a fair portion of NOS enthusiasm.

An inexpensive nos 12au7 type will almost always sound better than a new production tube of the same price. An expensive tube like an Amperex 7316, no contest. Look for reasonably priced nos. You'll be glad you did.

I’ve got a good assortment of these nos premium 12au7’s and 12ax7’s so I match them up as accurately as I can with my Hickok tester and use them that way. I really hear the difference in brand and era but not positive the matching is so critical but most experts would probably do what I do given the choice that I’ve accumulated 

people posting seem to be getting confused, referring to 6dj8 tube variants and such, when the op is specifically asking about 12au7 tubes and their equivalents

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets - no need to play with the relatively grim and unreliable chinese and russian current production when so many nice old stock ones are around

having said this, the 6dj8 types -- especially higher end dutch or uk cca ecc188 variants, what have you, that is a different universe, an entirely different discussion about value, availabilty and affordability

What are your favorite 12au7 type NEW production?

What amp? What purpose? What circuit? What music? What room? What system?

ALL sound different in different places. The validity of most opinions is ZERO.

And after how many hours as they change from first turn on...

Thanks to all for all the interesting posts.

It seems that matched is the way to go, but as I don’t want to spend top money on NOS tubes I will to manage with NEW production tubes.

What are your favorite 12au7 type NEW production?

FYI, I really haven't enjoyed any newer tubes, all of my favorites are NOS. I do use matched tubes for each channel of my 2 channel amp.

For the money, it is very hard to beat 1960s RCA "Clear Top" tubes; you can usually find them for about $20 or so each and they are terrific.

If you want next level it will cost you, I really enjoy Amperex tubes. My favorites are Amperex 7308 PQs, Amperex 7316 "Long Plates", Amperex 6922 PQs, and Phillips 12AU7s.

Everyone should figure where the bottom line is located and how it works.

It's extremely simple and safe to assume that dealers pragmatically label the tubes they sell to you as matched while in reality it's just a tube and sometimes even cigar is just a cigar.

12AU7-based mu-follower preamplifier stage driving a 100Wpc (into 8 ohm), class-D, solid-state power amplifier

A mu-follower has plenty of gain which has to be padded down to drive the Hypex UcD-180 Class D. Weird.

from stereophile’s review of the sphinx v3

Description: Hybrid integrated amplifier with 12AU7 tubes in line stage and class-D output stage. Power output: 100Wpc into 8 ohms (20dBW), 200Wpc into 4 ohms (20dBW). THD: <0.1% typical, <1% at rated power. Frequency response: 5Hz–20kHz, ±1dB. Input sensitivity: 1.0V RMS. Power requirements: 115/230V–50/60Hz.

12au7 pair is in line stage, not phono stage (which is solid state)...

...not to say that matching and low noise are not important, but just significantly less so than if it were in the phono stage

The Sphinx likely uses tubes for the phono section, so low noise is paramount.

For maximum RIAA fidelity and channel balance, the g1/g1 and g2/g2 sections need to be well matched, assuming the same topology for each channel.

The big fly in the matching ointment is that tubes seldom match across the entire operating range and matched tubes are matched in a matcher, NOT your amplifier and thus operate under totally different conditions. Tubes matched on one matcher may have very different numbers on another matcher.

Tubes matched today aren't matched tomorrow as they age at different rates.

See ieLogical Rolling

It's always important to match triodes 1 and 2 in a tube that is run in stereo. While triodes that are off by 10% may not hurt anything you will hear the imbalance. If it were just a matter of one triode having higher gain than the other you could adjust the balance control to fix it. But there's more to it. Each triode has it's own frequency response curve and selecting tubes with curves that are as closely matched as possible ensures that the left and right channels reproduce frequencies at nearly the same amplitude. Without this you will hear smearing of the image from side to side and a wandering in the image when a vocalist or instrument moves up and down the scale. So in order to keep a vocalist centered as she sings and a trumpeter locked in one place, the tubes need to be matched. I use an old TV-7 tube tester to see if my triodes are matched but it really only tells me that they are matched at 60Hz because that's the only frequency that it tests at. If you use a curve tracer or an Amplitrex tester you can see how they are matched from 20Hz - 20kHz. Getting as good a match as is practical is never a bad idea.

Most preamp circuits are run class A due to low signal levels. You want them matched for gain and screened for low noise, again because the signals are low at this stage.

On my Audio Research SP6B, the individual tubes can be biased, and it definitively improves sound quality. 
 

+1 re Brent Jessee, excellent guy, my matched Raytheon VT231’s and CBS/Hytron JAN 6S7N’s are wonderful, and he was a knowledgeable pleasure to work with in tube selection. 

@tomcy6 - Bob does some great work. He used to do Tube Only repair and customization and has his own patented circuit designs. He lives a mile away and has done some repairs for me even after he was building the new Pres. It's a nice sight seeing 6-8 of them on the bench in progress.

Use matched sets. I f not you'll be listening, thinking how good it sounds, then you'll wonder how it would have sounded with matched tubes.

i would always go for matched sets when they appear in serious hifi gear

of course testing does not guarantee the electrical match seen on the tester will persist over the lifetime of the tubes in use, but it is a much better starting point than starting with wildly mismatched ones at the get-go

that said, i agree with others who have said that old stock 12au7’s are still plentiful, and not very expensive

i have over a hundred of them in matched sets collected since the 80’s, mostly american made ones (sylvania, rca, ge and so on) ... happy to assist if anyone here (in the usa) needs some

I’ve never seen that option on preamp tubes! Have you?

From Backert Labs, who make only preamps:

Our Rhythm, Rhumba Extreme, and Rhumba Xphono preamps automatically and continuously adjust the bias that is applied to your tubes, ensuring correct bias at all times.

Adjustment is automatic, requiring no action on the user’s part.

Why is this important? Each pair of tubes requires slightly different bias. The result of our automatic bias adjustment: a circuit that brings out the very best from every tube you insert.

So Preamps Require Tube Biasing?

Actually, no. None of the other tube preamps on the market today, as far as we know, adjusts bias. And they work just fine. In fact our own Rhumba preamp does not adjust tube bias.  And it sounds great. This is because the tube bias, set at the factory, works perfectly with the stock tubes that we supply.

When bias adjustment matters is when you experiment with other brands of 12au7 tubes. Or tubes that are compatible with 12au7, such as 5814A, or CV4003. Some of these will have unusual bias requirements, which can make them sound “not their best” if those unusual bias requirements are not met.

Visit www.audiotubes.com/12au7.htm where everything he has is listed, prices and described very well. Then email Jesse Brent. He offers a 30 return policy.

why dont u want matched, balanced NOS? 12AU7 are so, so cheap. RCA cleartop are $20 a pop, and theyre one of the favorites. . 

I always buy a matched pair when there is one per each left / right channel as in this case.  

Also for preamp tubes I request them to be screened for low noise.  

@ jeffstrick

"when you have bias capabilities there is no reason to match tubes."

I’ve never seen that option on preamp tubes! Have you?

when you have bias capabilities there is no reason to match tubes. 

you don't need to match small signal tubes and unlikely you need to match even power tube.

I'll take matched thanks...    I say this confidently because I have a tube tester and have had some new tubes that many would consider "junk"    With a tube like 12ax7 , the tube's performance has a lot to do with whether each triode section is close to the other.   There are two triodes in one glass envelope.     

The last few times I bought tubes I did pay for matched triodes, pairs, and screen for low noise and they were exactly as paid for.   Excellent,  quiet , super strong emissions. 

Agree with vinylvalet…i have heard the same from several sources as well. Tube sellers charge a premium for high test results that may or not be a true indication tube health or SQ and say different. Buying tubes new or old stock is always a risk but test results are helpful for minimizing that risk. I much prefer old stock preamp tubes for their SQ and durability.

Check out this link that explains more:  https://geekmusician.com/do-preamp-tubes-need-to-be-matched/

Choice d) Matched, balanced pair of identical nos tubes. And make them Amperex 7316's.

OP I'd go with choice a from your post.

It depends on the circuit design. In most cases, no, you don't need matched pairs or matched triodes within the each tube.

Honest tube dealers like Jim McShane will say the same thing.