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)
10-15-14
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." |
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. |
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. |
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. |
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". |
Thanks. Listening some more - the conclusion is the same, I like this. |
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. |
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.
Ø
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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.
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In other words, the RCA 6AS7G tube has worked excellently over four years now. I have associated it with a plus in the overall sound of the MA-1 amps. Set and forget.
Ordering a large quantity of these (28 in my case, from Brent Jessee) is a risk, of course. You may get a few problem tubes (even from reputed dealers), but these are easily spotted, showing up quite soon (arcing, strange bias behavior). You can spot them also if you have a tube tester.
In my case, the RCA failure rate is 10 percent, no worse than with Russian NOS like Winged C. Stock tubes from Atma-sphere have also failed now and then (not frequent - 5 percent maybe). It is part of the tube scenario.
By the way, a few of the RCAs are replaced by Winged Cs in my amps, working well together ;-)
The improvement from stock output tubes to NOS is maybe not so obvious, then and there, compared to driver tube changes. It is more long term.
I am not sure of the lifetime of the RCA 6AS7G tube. The RCAs have been running "hot" for maybe 2000 hours in my system over the last four years, plus some "standby" hours that don't affect the lifetime.
I end up by thinking - no wonder users buy NOS tubes for these marvellous amps.
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A little update:The RCA 6AS7Gs have worked fine for the last two years - very stable - nice sound - happy with this set (although I had some failures in the beginning, despite preconditioning them).
Driver tubes: I have the four tube (long chassis) MA1 v3.2. Now trying RCA 6SN7GTA in V1,
RCA 6SN7GTB in V2,
RCA 6SN7GTB in V3, and Sylvania in V4.
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