Is there a strategy in preamp tube placement?

The loose "rules of thumb":

• Upstream / input tube slots (e.g. "V1"), and slots that contribute gain (as opposed to follower or buffer tubes) are more sensitive to tube rolling, and you should use your best tubes here. But then there are also mu followers, which do both. You also want to be careful to choose very quiet tubes for V1.
• The older 1940’s VT-231 and early-1950s 6SN7GT tubes are generally sweeter, "airier", and better sounding than later GTA and GTB variants. This is where the 6SN7 gets its beloved reputation ("king of tone", etc). Unfortunately, they also tend to be noisier. It’s hard to find a quiet Ken-Rad or Tung-Sol black glass VT231, no matter how sweet they may sound. Microphonics are particularly a big issue here. So it’s a catch-22. You want to use the sweetest tubes in your V1, but then noise issues might make this a poor fit. I’ve generally been able to use old 6SN7 tubes in V1 of power amps, but NOT in preamps, due to noise. If you have to find a quieter tube for V1, you can try early-make GTA or GTB tubes (1950s better than 60s). They are a LOT quieter. I like the Sylvania tall-bottle "chrome dome" 6SN7GTA, but still prefer older 6SN7 tubes. Or you can try modern Russian / Chinese tubes.
• 6SN7 aficionados LOVE to match 2 different makes (where possible), rather than stocking all slots with the same make (e.g. Tung-Sol round plates in V1, Sylvania VT-231 in V2). With 6SN7 tubes in particular, this seems to sum up the positive sonic attributes of each make with little downside.
• The modern Russian EH 6SN7 and Tung-Sol GTB reissues are solid tubes. They’re not the most refined or sweetest sounding 6SN7, but they do a good job, and their transconductance is going to be 20-25% higher than any vintage tubes you find - VERY strong. I believe these tubes are a natural fit for output and driver slots (e.g. driving KT88 or KT120 power tubes). They have a clean, punchy sound - "rock n’ roll". They can also be selected for low noise & microphony. I don’t love them in V1, but if you have too much noise with the older types then you can try them here.
• Everyone who’s been in the 6SN7 game will develop favorites. There are some patterns and general agreements on what’s better or worse, but nothing’s written in stone. I really like the Tung-Sol Black Glass Round plate VT-231 - others will say they’re way overrated! Some really like the NOS Russian "Melz" tube, but I haven’t heard them myself (said to be the Telefunken of 6SN7, if Tele made this tube).

Fantastic post by @mulveling  and that's a very nice preamp @coachpoconnor 

mulveling-
I very much appreciate your response.

I have a Tung-sol 6sn7gtb in the gain stage and the Linlai E 6sn7 in the buffer spot. Down stream I have a SIT-3 and Cornwall lV’s and it is amazing how swapping the few tubes I have, affects the sound, so coming up with a strategy is important.

jond- thanks!

@coachpoconnor yes, in my SLP-98 and sparing you my vintage 6SN7 tube trials with RCA and Sylvania Black Plates I own and tried, I’ve been experimenting again with newer tubes some.

• TJ Full Music 6SN7s in the all four spots (most transparent, more detailed)
• Psvane CV181-T MKII (6SN7) in front spots and TJ Full Music in the rear (smoothed over a bit too much for my taste, yet still nice)
• TJ Full Music in the front spots and Psvane CV181-T MKII (6SN7) in the rear. (nice balance, best over all, smooth, yet detailed, musical)
• Tung Sol 6SN7GTB in all four spots (too veiled, weighty bass, smaller sound stage, a little grainy, not preferred) my trusty backup test tubes at best.
• EH factory 6SN7s, a little lean, sitting in their original boxes stored away for the day I resale my 98 preamp down the road. 

@mulveling Has gave a very good base to prepare for a investigation.

A very experienced Valve user, gave myself the very layman advisory, the most Upstream Tube is the one that sends on the signal downstream, the more confidence there is in the quality of the signal at this stage will usually deliver significant SQ that can be built on by further investigation into tube permutations

I have carried out a fair quantity of 6SN7 Tube Comparisons.

I settled on the KR Black Glass VT 231, as the best attractor for myself.

I then learned of certain individuals making claims the Linlai E 6SN7 with approx' 100 Hours usage life has compared favourably to the KR VT 231. The reports being made on these Tubes are generally good and have got my attention.   

+1 @mulveling  couldn’t have said it better myself. Great info!

@mulveling 

Bravo!
I’m going to save your post for future reference.

All the best.

JD

@coachpoconnor

Great preamp! It’s on my list to replace an old ARC SP-9mkll.

Question, did you get the phono section  built in? If so, how does it sound?

All the best.

JD

@pindac "The reports being made on these Tubes are generally good and have got my attention".

For sure. After trying various matched pairs and matched quads of vintage over a decade, along with several loaners from friends, now mothballing them away in storage and going through some of the new boutique tubes coming available the past 1-5 years has been worth it. Following these same engineers from factory to factory design teams is interesting. Linlai are next for me to try.  Some of the better quality and better sounding tubes coming out is a nice option to have. I’m still in the 1-2+ year longevity evaluation phase on my last three quad sets. Time will tell.

The best tube placement I have ever seen is in their sockets. 

I settled on the KR Black Glass VT 231, as the best attractor for myself.

I then learned of certain individuals making claims the Linlai E 6SN7 with approx’ 100 Hours usage life has compared favourably to the KR VT 231. The reports being made on these Tubes are generally good and have got my attention.

@pindac , the Linlai Global Elite E-6SN7 are the tubes being praised and compared to Ken Rad VT-231. Available only through Linlai factory direct and Grant Fidelity.

The E-6SN7 available on Ebay are intended for the Chinese market. The Global Elite are for export to the US.

The Thread that caught my attention, which has now expended quite considerably with posts since first discovered, is in the link.

 Audiogon Discussion Forum

@pindac 

I was one of the early buyers of Linlai's 6SN7. Due to a lack of information at the time, I purchased E-6SN7's from an Ebay dealer. I was very active on that thread as members learned that there were indeed two different 6SN7 types (as stated on the Linlai website). As the tubes burned in, it sounded like they may live up to the hype. But after 100 hours they sounded dull and lacked the realism that the Grant Fidelity tube users were reporting. 

If I knew then what I know now, I would have paid the higher price of the Global Elite with the vertical Linlai logo on the glass.

Lowrider57, On tubes most of the time you get what you paid for, I agree with you, after paying premium price for my globe 6sn7 at Grant Fidelity , it made me realize what a high quality tube is all about.Though I did have luck buying tubes from Chinese 6sn7 dealers o  Pavanedirect and HiFi ...

@lowrider57 The advisory is registered.

When I enter into the exercise of re-visiting 6SN7 Tubes used on my system I will be cautious of the Linlai E Types I buy into.

Especially as I have also discovered the option to use an adaptor for the Pins and use them on a owned Phono- Pre and DAC which are using early 60's Vintage E88CC Tubes.

The additional comparisons for myself, will be a voyage into the unknown. 

The only principle that holds water is to put your best tube in the gain stage. The last tube before the output jacks is almost always a cathode follower. Cathode follower does not add gain and therefore has little effect on SQ. Except the CF by its nature can add a coloration that won’t be entirely overcome with even the best sounding tube.

while I think this talk about tube rolling as if it was a panacea is blather, I too prefer the KenRad VT231 over all other 6SN7s. But they’re microphonic.

@curiousjim - A buddy came over yesterday and we installed 4 of his olderTelefunken's in the phono stage in place of the Electro Harmonics. It was really really nice.

@lowrider57- I bought my Linlai's from Vivatubes, so I'm on the fence about buying a 2nd set from Grant Fidelity or finding a set of Ken Rad's

Presently, I have a set of Tung-sol's in the Gain position and the Linlai's in the Buffer spot. I still need to experiment a little more.

@decooney - The Full Music seems reasonably priced, might have to experiment.

I too have a Cary preamp that I bought earlier this year.  I got the SLP-05, and it has a pair of 6SN7 tubes for the balanced input buffer, and 2 pairs of 6SN7 for the left and right gain stage.  The stock EH tubes have good details in the treble and decent slam in the bass, but I found them to be a little too bright for my system.

So I bought 3 pairs of NOS RCA black plates to replace them all.  The RCA's are much warmer, less details but no harshness at all at the high end. The bass does get pretty low, but lack a little bit of slam.  Overall, I found them to be a little bit too dark.

So I changed the pair for the balanced buffer back to the stock EH tubes.  It sounded much better now with that setup (EH in the buffer, and RCA in the gain).  It restored some details on the high end, but without the brightness, and just a tad of improvement on the tightness of the bass.  So I kind of agree with @lewm that the tubes at the gain stage seem to have bigger impact on the SQ.

Anyway, I also recently bought some Ken Rad VT-231, based on all the praises I read here, and sure enough, they have very bad microphonic.   One minute into the first song I played with these KR, there was a sudden loud hum coming out of my speakers, and I ran to lower the volume down to zero, but the hum was still there.  I ended up having to power off the preamp to stop it.   I tried playing some songs again after a few minutes, and by chance I noticed a loud knocking sound coming out of the speaker when I just happened to tap the volume knob while trying to adjust the volume.  I then tried tapping the surface areas of my preamp, and every time it would be amplified and heard through my speakers.   I ended up returning them to the dealers and asked if he can find me some without the microphonic, but I haven't heard back.

Questions to you guys with the Ken Rad with microphonic.   How do you guys deal with this issue? or do you simply just live with it?   Thanks.

Hey @coachpoconnor, how are you liking the Linlai's?  I've been thinking about trying a pair also, but haven't pulled the trigger yet.   Also the Elite 6SN7 might be a little bit too tall for my setup, so I'm also considering the globe shaped ones available in Grand Fidelity, which are $400 a pair.   It's a lot of money to spend without hearing them first. Thanks.

re: " The Full Music seems reasonably priced, might have to experiment."

To @coachpoconnor, I went with them long before the Linlai came out, and was tired of chasing quality matched pairs and quads of vintage 6SN7s any more. A SET/Triode obsessed gear friend of mine turned me on to them a few years back. Its worth following the other 6SN7 thread on Agon for more info. I would not say they are better than Linlai, yet I do like the TJFM better in some ways then the psvane CV181-MKIIs, and vice versa in other ways. Different sounding tubes, comparing them to each other.

That’s where I started mixing them within the SLP-98 for an enhanced result. Like mixing in a little butter and lemon for a good pasta dish, hahaha. :)

If you have Linlai now, will be interested in your feedback if you mix them with psvane or TJFM later on. I started doing this to have at least 2-3 other type quad sets in reserve while I mainly keep my vintage stuff tucked away and rotate them in every once in a while. Honestly, no need for it after I got the TJFMs in rotation, and they fit and seat down very well in the 98. PM if interested, I get them from their largest distributor overseas, with fewer middle-men and handoffs in shipping, helps reduce shipping damage some, and this dist packs them well layered in cotton, good boxing. Cheap insurance actually.

They learned this years back after a series of tubes failing after poor packing/shipping. Mine have 2yrs run-in on them now. So far, like mixing psvane/tjfm. Having another quad of Linlai will be good. Thx

With KenRad, I've had problems with microphonics that were not totally curable, even in my Atma-sphere MP1 where the tubes are entirely enclosed in the chassis and my MP1 is 22 feet away from my speakers with a couch in between.  However, the problem was "tolerable".  Then I switched to RCA VT231 gray glass in the gain stage.  They're not quite as terrific as the KR but less microphonic, at least the pair I've got.  Much better in that regard. In my Atma amplifiers which sit next to the speakers, I use 12SN7s or 12SX7s (6SN7 with 12V filament); for some reason these are not microphonic at all.

Questions to you guys with the Ken Rad with microphonic. How do you guys deal with this issue? or do you simply just live with it? Thanks.

Yes, I can confirm Ken-Rads tend to be the most microphonic and can have come-and-go noise issues. Vibration control tweaks, tube dampers - these have no effect on such a problematic tube. The only "solution" with such a tube is to move it further downstream. The more upstream it’s positioned, the more gain it has stacked after it, amplifying all that noise crap (or in the case of microphonics, making a stronger feedback loop!). Having high sensitivity speakers acts like extra downstream gain, and exacerbates the issue. The only exception is a tube right before a volume control, which acts like a large negative gain in most systems, but it’s rare to find a slot like that (maybe cathode follower output in a tube phono stage).

With Ken-Rads, I’m only consistently able to use them in power amps. Almost never in preamps, no matter the slot. And DEFINITELY not gain slots in the preamp. A preamp slot in an integrated amp doesn’t count as an "amp slot".

@xcool

I own two pairs of Ken Rad VT-231 black glass and a pair of clear glass (1945). When purchasing these tubes or others from the 40’s, it’s imperative that the dealer offers testing for noise and microphonics. Andy from VTS, Kevin Deal, Brent Jessee (for a fee) all noise-test their tubes. But there’s no way to tell if a tube will become microphonic at some point in its lifetime. All three pairs of my KR’s have remained noise free. But one of my beloved Tung-Sol BGRP’s went microphonic after 3 years. I've been using these tubes in gain stages of my preamp and amp.

There are many causes of noise from a vacuum tube and microphonics is only one of them. You can test for the other kinds prior to purchase but it is hard to predict whether a tube will be microphonic or not in your home system, because circuitry, cabinet damping and/or direct tube damping, proximity to speakers, typical listening levels in terms of SPLs, socket design, etc, all contribute to the problem or to its prevention.  That said, some tube types are just more prone to the problem than others. In the case of octal base triodes, like the 6SN7, 6SL7, etc, those are just more likely to be microphonic.  Some say this is due to the relatively large size of the glass envelope and the fact that the plate structures are more or less prone to vibrate in the large volume environment.

Yeah largely sized tube elements combined with lots of gain is a challenge. It’s also hard for those flimsy mica spacers to tightly hold down the grid/plates/cathode spatial relationships enough versus the gain factor, especially after all these decades. Ken Rads in particular often have a nasty little audible internal rattle you can excite with a tap to the glass (this is with the tube in your hand, not plugged in). Those tubes are REALLY gonna give you a headache in preamps.

Even in 12AX7 the short plate variants are sometimes thought to be less susceptible to microphonics. 12BH7 as a 12AU7 sub is another example where the larger plate structure (12BH7) leads to big headaches with microphony.

Later versions of 6SN7 had better bracing and plate designs to mitigate these issues.

Thanks @lowrider57, I actually did purchase the Ken Rad from Brent Jessee.  Great guy to deal with.   My first set of RCA was purchased from him also.   I was going to hear from him if he's able to replace those KR that I sent back with something low noise and non-microphonic, but I haven't heard back yet.   He actually never mentioned any extra fee for noise and microphonic testing.   I wouldn't mind paying the extra if he can do that.

Anyway, reading some of the comments here, maybe I should just forget about the KR for my preamp.  The RCA black plates that I have are very robust.  No noise or microphonic, and sound pretty good.  Maybe I should just stick with those for now.  

@xcool 

The noise testing service is somewhere on the Brent Jessee site, $10/pair I think. You have to request it in your email to him.

With 6SN7s from the 40's or 50s, I always order noise testing. In Brent's description he may say a certain tube is low-noise, then it's not necessary to pay an extra fee. As @mulveling stated, later generations of tubes used different internal designs to mitigate microphonics. Some military-grade tubes are "ruggedized" with extra support rods and micas to withstand shock and vibration. With 6SN7s, there's a chance these tubes may be less microphonic.

Thanks @lowrider57 for the information on the fee.

I'm still fairly new in tube rolling, and learning a lot from this thread.  Thanks!

These days I’d also be leery of counterfeits of tubes that are now 70 and more years old. The best sounding KRs are the black glass variant. You can’t see what you’re buying.

     YEP (Brent charges $5/tube for noise testing)!

     A vid, describing his testing method, can be found just into the the tube description portion of this page:                       

                     http://www.audiotubes.com/6sn7.htm

"These days I’d also be leery of counterfeits of tubes that are now 70 and more years old.

The best sounding KRs are the black glass variant. You can’t see what you’re buying."

     The 1940s, Ken-Rad, VT-231/JAN-CKR/6SN7GT has bottom gettering, a very unique top mica and support structure, including copper posts*, which are plainly visible (blacked glass or not).

     I’ve never seen a counterfeit CKR proffered, though: I’m certain I’ve not seen everything for sale out there.

        On the page linked previously; Brent has a three part vid, on spotting genuine NOS tubes, worth viewing by any seeker.

   *ie: https://www.ebay.com/itm/185479311423?hash=item2b2f6db03f:g:6~QAAOSwGRliuJhB

     btw: Crazy price on that linked, eBay pair of KRs (to me, anyway), BUT, then there’s:

https://www.ebay.com/itm/174924762007?hash=item28ba540b97:g:1UYAAOSwfj1hNNVb  (PLUS SHIPPING!)

     That French seller is clearly very proud of his tubes!

I bought my wide variety of 6SN7s and 12SX7s back in the 80s and 90s. Thankfully, I am not in the market.  I would agree that counterfeit 6SN7s would be easier to detect than counterfeit 9-pin miniature triodes, e.g., Telefunken, but there are many among us who don't know what you are talking about when you use terms like "bottom gettering, a very unique top mica and support structure, including copper posts*".  So, I am just saying know your source.

     I couldn't agree more, that a tube buyer should be familiar with their seller.   BUT: that's seldom the case, with the first-timer or neophyte.

"...but there are many among us who don't know what you are talking about when you use terms like "bottom gettering, a very unique top mica and support structure, including copper posts*"."

     Perhaps: that would explain the existence of this website, it's educators and an Internet, replete with pictures and vids*, to instruct/guide such, in their pursuit of the hobby and better sound.

                                            *ie: see above

         Of course: CAVEAT EMPTOR will always remain a prime directive!

                                          Happy listening!

In the world of diminishing resources.

Especially in the area of Vintage Tubes and where certain ones from this era, are desirable and have a rarity.

I don't see many revealing their pearls to show how to select the best offerings as they appear. A knowledge of the desirability of the Tube is usually enough.

The KR VT 231 Black Glass or not is a good example from this thread, the tube is revealed, the concerns about quality are shared. 

The rest is Caveat Emptor for a inexperienced or not well connected buyer.

I am such a individual with limited experience. I am fortunate to have a friend who is second generation Tube Collector and what I will refer to as a Specialist.

All Tubes Purchased are pre agreed as part of a sale to be tested by this friend.

All vendors have to agree to accepting the tube returned and monies refunded, if the tube is testing quite different to the seller supplied Test results when Tested at my end.

Fortunately this is a method that has worked out on quite a few occasions, with the odd anomaly and refund request made.

It does take a little time to assemble a selection for tube rolling purposes.

Fortunately on occasion, a selection of Tubes have been loaned by this friend, for the purpose of Tube Rolling and selecting a permutation that has proven to be quite attractive. My Two Phonostages and DAC have all been subjected to evaluation through the use of loaned Tubes. 

The friend has demonstrated Tubes in use with different usage life left in them, a Tube with a reading with approx' 30% down on the Manufacturers Optimum Reading can sound quite nice, it is only when an Optimum Reading Tube is used as the comparison, does the tube get separated for not having the qualities that really show out.

In my recollection of an assessment of two same Branded/Model Tubes, a Cold Optimum Measured Tube stands out with immediacy as an attractor, much more than a Heated Tube with a 30% reduction in usage life.

This was also experienced with a Pair of ECC81's on my phonostage, I was loaned as a stop gap, two tubes from the Brand I was interested in, that according to the friend who owned them, were almost at the end of their recommended usage.

When I finally was in possession of Two Tubes very closely matched and at the manufacturers optimum measurement, the exchange of Tubes, was to say the least, Jaw Dropping, music that was present, took on a whole new voluminous presence, along with the Performers becoming quite distinguished and very much in the room. 

All tubes to a certain point of degradation will produce a Sound, it is the remaining usage life within the Tube, that will allow for the Tube to be an attractor and impressive, the nearer optimum measure, is in my view, the place that can really show where the desirable qualities are to be found.