Atma-sphere amps best power tubes

This question has been debated before on A-gon but without a clear onclusion. I wonder, is it worth it, to upgrade from stock Russian or China output tubes (6as7g), to American NOS tubes?

It seems that everyone agrees that upgrading the Atma-sphere driver tubes from stock Russian/Chinese to NOS is well worth it. This is my experience also.

I am wondering about changing the output / power tubes too. I wonder if a change to NOS is well worth it also in the output case.

It seems likely, judging from my other equipment testing.

My Audiotailor Jade OTL headphone amp uses 1 6asg7 and 1 12ax7. No surprise - it sounds better with a good NOS 12ax7 compared to Russian/Chinese stock 12ax7.

More surprisingly, it also sounds clearly better with a NOS 6as7g output tube (General Electric US NOS). The improvement is largest with the driver tube but not so much behind with the output tube. Almost 50 50.

A lot of output tubes are involved - 28 tubes in my MA-1 amps. Changing them all is costly, and so I would like to know some user experience before I go into this.
How many good roughly matched 6AS7G US made or other NOS tubes can you assemble. I also have a headphone amp which uses the 6080/6AS7G/421A etc. tubes. I can't recall having a large number of special 6AS7gs offered for sale. You can of course find different Soviet era tubes.
I am curious as to why you thought changing the output tube would nothave a big impact on the sound. I have been on a crusade telling any who care to use tube power amps.
My main system didn't have it's magic sound after years of switching and tweaking, until I switched to tube monoblocs.
O_holter, Ralph has always commented that he used the Soviet 6AS7 tubes, and now the Chinese, because he could never find US made 6AS7 tubes that were as reliable or long-lasting in his circuit. With the changes he made a few years back, his opinion may have changed. Have you called him?
Rushton - Yes it seems that Ralph is now more positive to using American 6as7g tubes, at least in recent amp versions (I have 3.2). In another thread he wrote about some customers reporting good results. Preconditioning is important. There will probably be failures, but that is the case with new Soviet and Chinese tubes also, in my experience.
Mechans - thanks, I agree, in general better tubes means better sound. Yet it would be interesting if anyone has actually tried a full set of China/Russia versus a full set of US output tubes in an A-S amp, and could describe the sound difference more precisely.
I found some comment in earlier threads.
06-12-11: Entrope
"As the owner of Atma-sphere M60 mkII.3's I find the the RCA 6AS7 available and not to pricey. They sound much better than the stock Russian tubes. In speaking with Ralph Karsten he indicated the amps probably had a somewhat greater power output with the American tubes over the stock tubes. He indicated as much as 20%."
See thread 1307834958.
Also there was a thread on Atmasphere output tubes in October 2014, although I cannot find it now. I copied a few of the posts:
"atmasphere 6as7g output tubes.
Time to get some new tubes, I know atmasphere does not recommend nos tubes. I really have to say my amps would not sound the same without nos input tubes. I was wondering if there are any opinions regarding using nos or vintage tubes for output tubes."
Toothman (Threads | Answers | This Thread)
Responses (1-17 of 17)
10-16-14: Brf
"It's your amp and it's your money, therefore, as long as you are using the same tube type, knock your socks off and roll the NOS tubes."
Brf (Threads | Answers | This Thread)
10-16-14: Atmasphere
"The American 6AS7Gs can have issues, although we have found that the 6AS7GAs are the ones that are most problematic.
Here is what we know about the American tubes so far:
1) you get best results if your amplifier is a Mk3 or later.
2) If NOS, the tubes should be preconditioned for 4 days and 4 nights. This is done by placing them in the amp and putting it in Standby only for that time. If you apply B+ during that period the preconditioning process is ended.
Preconditioning can double the life of the tubes, help restore a better vacuum by activating the getter, and will also reduce the possibility of premature arcing.
BTW this process applies to all output tubes, assuming they are new/untested or NOS.
I would regard the use of American 6AS7Gs as experimental as you may run into premature arcing, but some customers have had excellent results. I think a lot depends on the tubes, if they are really NOS, that sort of thing. However- stay away from the GA varieties- they won't work."
O_holter, Great information collected from Ralph. Thanks for collecting it all into one place and sharing it. Sometime I'll have to re-tube my MA-2 amps, so you can imagine I'm likely to be even more cautious than you!
Thanks Rushton! A pleasure.

Besides buying some US tubes to try out, I am investing in a MR-1 tube tester from Helmut Beck, Germany - custom setup so it takes all the tube types in my system. I have no less than 87 tubes alltogether in the system (blush! I had not planned this).

I've had quite a large failure rate with 6as7s and this seems to be a common experience. My hope is that the tester will at least help avoid putting bad tubes into the system and that this will mean less repairs, less damage to other components etc. Hopefully the tester will also be of help getting the best sound, combined with listening.
Just be cautious about relying on the testing with the 6AS7G tubes. Again, recalling what Ralph has mentioned to me over the years, typical tube testers do not measure a 6AS7G in the same manner as is used in the Atma-Sphere circuit. Perhaps the MR-1 from Helmut Beck does so.

I keep hearing about failures in these power tubes. In 14 years running the MA-2, I've had only 4 tube failures with the Sovteks installed. Many of my tubes are still orginal with thousands of hours on them. I suppose my time is coming due. ;-)

And, I now feel absolutely free-spirited with only 84 tubes in my system!
84 tubes only - you are on a diet I suppose?
I read somewhere that testing the 6AS7G is one thing - another is how it actually performs. (And - how it actually performs in an Atma amp).

I had the amps to repair recently and the repair man Hans Kise tested while I looked, finding that about 40 per cent of the 28 output tubes measured non-optimal. He had the amps lying on the side, bottom plate removed, and used a multimeter on the connections of each tube in the amp itself (not a tube tester). Two days later he was on his way to trash the non-optimal tubes when I told him to wait a little - he managed to salvage them, before the garbage collection. I want to test them some more.
I keep hoping that Ralph and crew will follow thru one day on the oft hinted at 6AS7G tube tester that they were going to build. A lot of us would really like to put to bed once and for all the issue of whether or not our various testers are up to the task of RELIABLY evaluating our power tubes or not. A purpose built unit would be a godsend.
Hi Acresverde - I have bought a RM-1 tube tester from Beck Electronics in Germany, custom setup so it can test 6AS7G (among others). I have not received it yet, so we shall see, does it do the job. My impression, living with 28 of these tubes for some years, plus reading others' experience, is that they are unpredictable. It seems that it is not so easy to tell if a tube will arc or not. I have had "tested" sets of 28 tubes, yet with quite a few failures, here also.
Burning in a set of 28 RCA 6AS7Gs right now - following Atma-sphere advice, 72 hours on Standby, before turning the amps On. I hope they work OK, and give the same sonic improvement that I have heard other places, changing from stock Chinese/Russian versions.
Will be very interested to hear you assessment of the sound quality, O_holter.
As shall I :-)
I'm pre-conditioning 6H13C's at the moment.
Best of luck with your RCA's!
Thanks Rushton & Clferrari. I am sure people have tried this before me but there is not much info on the web, since most of the focus has been on the driver tubes. It will be interesting.
After 60 hours of preconditioning I could not stand the silence anymore, and decided to give the RCA 6AS7G tube set a try. So I put the MA-1 amps from Standby (yellow) to On (red light). No misbehaviour or arcing so far, having played for three hours. Sound? Short version: not looking back, these tubes stay, my Russian/Chinese (Atma-sphere stock tubes) have now become extras. Tested with some favorite LPs, Can: Future days, Cohen: Ten new songs, Stranglers: Feline, Alan Parsons Project: Eye in the sky - all very good indeed. It is a bit of give and take though. The Russian may measure better, more top and bottom frequency, more upfront sound, but to my ears they are also fatiguing and hard. The RCAs may be more rounded off, but the musical illusion is better. Like my wife said, "they are more silent so you can hear more detail". Only trouble so far - some noise from 1-2 tubes in the right channel, off and on, seems to go away when I rap them, may need replacement.
I listened some more. If these 28 RCA tubes hold up there is no doubt, this is what I prefer. I am willing to foresake the strong points of the stock Russia/China tubes. Three main reasons. First, better musical illusion, in the midrange especially. Second, more musical drama. Even boring tracks sound less boring now. Third, more than with the stock tubes, the amps become chameleons. They shift according to the sound, the production of each track - a big plus in my book. So my main reaction is "I never knew this LP was that good". Like Elton John: Tumbleweed connection, things I've not played much. This is a good sign. I checked with some of the more "wool" sounding record I have, did they sound too closed in now, like one might suspect. Including Carlos Jobim: Wave (on Speakers Corner). But no, they sound good. Another plus in my book. I read somewhere that the RCAs would increase the output compared to the stock, but that is not the case for me. The only thing I miss is a bit more output and volume, "slam factor".
Good report, O_holter. Hopefully the RCAs will also prove themselves to be reliable over the longer term, which will then provide a great alternative!
Thanks. Listening some more - the conclusion is the same, I like this.
Well it's ten days later, has the perceived lack of overall volume and slam come back? Curious myself because I have a headphone amp that can use 6AS7Gs . Right now I am happiest with 5998s in there (so called "Domino" plates). I have use 6080s and preferred the RCAs. I had some 6AS7G variants but no RCA or other U.S. tubes.

Are you still using Sylvanias and RCA's in the 6SN7 positions of your MA-1's?

I am away travelling and also have some speaker driver problems (not tube-related) so it will take some time before I can answer these questions.
Finally I've had time to test my 28 6AS7G output tubes and about 20 extras, in my new Beck RM-1 tester. The measurements vary a lot (between tubes, and internally between sections) - all in all, quite disappointing, both for the RCA NOS set and my new stock russian (mostly Svetlana). 2 of the RCA tubes had one section dead, and 2 measured VERY low. No wonder I lacked some volume and slam. I have now changed these 4 into four extra RCA's that I bought, knowing that this was likely to happen. I actually bought 6 extras, but 2 of them were bad. It seems typical, regarding this tube.

I have also changed the driver tubes, taking out two Sylvanias that may have been problematic / worn out. On the mk 2.2 long chassis amps, the positions are not very intuitive, so perhaps other users may find the following information useful (checked with Ralph).

Position - tube type - function

v4 (front corner facing output tubes) – 6SN7GTA or 6SN7GTB – output section driver

v2 – 6SN7GT - sections should be matched – top half of the cascode voltage

v1 – 6BX7 (or 6BL7) - sections should be matched – bottom half of the cascode voltage

v3 (back corner facing power) - 6SN7GT - constant current source.

I now mainly use new tubes from Atma-Sphere that I got in 2013. They were hard-sounding compared to the NOS Sylvania I was used to, and I disliked them at first. Gradually they became, well, more acceptable. I use the A-S supplied General Electric 6BX7 in the v1 position. I keep a Sylvania in the v2 position, but use the the new Chinese brown-base 6SN7GT in v4 and v1.
O_Holter, Interesting report. The truth can be painful. I have been a tube hoarder after discovering that changing out the Chinese 6SN7 driver for NOS Sylvania GTBs (not even fancy pants tubes)in my first tube amp made such a positive impact on the sound. That was about 12 or more years ago. Now divorced I have my tube collection but few places to use it.
I have about 75 really good, some quite rare, 6SN7s in arms length at the moment-Feel free to contact me, if the rules allow it.
Here is an update on my RCA and other US NOS output tubes, over the last year. No problems at all - they all run fine. Adding to better sound. I am glad that I followed the careful break in procedure, described by Atma-sphere.

Why not Email Ralph at Atma-Sphere and ask the designer himself?
@don_c55 , he did that about a year ago.

Now that you have some nice NOS power tubes.  Why not, try rolling some of the 6SN7s you may be pleasantly surprised.

Try dome Sylvania Ws note not WGT ,  These have the renowned 'chrome dome'.  They are expensive but are very good.  The short bottle is relatively more common than the talls etc. and have been selling for unusually low prices of late -about $50  or slightly more for ea. .
Updating experience with NOS output tubes in the MA-1 amps (mainly RCA 6AS7G). I have had zero problems, no failures, over the last half year. This NOS set has now been running for close to two years. I enjoy the sound.
It's a very interesting combination of input tubes . Obviously highly amp specific. If you want clean crisp almost SS sound from a 6SN7 try  old stock Hytrons, avoid the CBS Hytron.
I have to chime in on this....

I just put some Shuguang CV181-Z tubes in my AtmaSphere UV-1 pre. Best 6SN7s I have heard, and by a mile.  CLARITY.  I also run M60s and will be trying to figure out if they'll fit. They are not shaped like typical 6SN7
@ bigboltz. Does the UV-1 transmit the character of the 6SN7S  really well when you roll them?