The power output of the tubes has little to do with the bias point. If anything, reducing the bias current will cause the amp to make slightly more power.
The RCAs are properly biased in the amp and will hold up alright if correctly preconditioned (which is about 4 days and nights continuous, whereas the Russian tubes seem to only need 3 days and nights). But this only applies to the 6AS7G and **not** any of the variants (like the GA) which simply won't hold up no matter what you do.
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Got it Ralph, which with the RCA with the same bias they will produce a little more power, run hotter and possibly demand more current for the same voltage bias correct? and also be more prone to failure maybe?
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I guess Svetlana vs RCA you have to compromise on something, and I also
guess your "bias" is tailored to the Russian tube not the RCA
They both bias to the same point. |
Conditioning completed, the tubes which were arcing before still arcs, with the exception of the GE, which is a G not a GA but I don't trust it so I retired it. Listening to it, I can't tell if the RCAs are better,
More powerful yes they are, I can run the middle switch on the MA-1s on the down position and this is with only 12 tubes
More transparent, could be but I can't confirm need to listen more
BUT highs seems to be recessed and veiled a little, less detail which is a big drawback IMO
I guess Svetlana vs RCA you have to compromise on something, and I also guess your "bias" is tailored to the Russian tube not the RCA
I really don't like to give up on things but in my case since I have high sensitivity impedance speakers it is not worth the trouble going with the RCAs, this is a preliminary conclusion, I do have to test more.
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Once B+ is applied to a new tube, the preconditioning process is ended. So You don't ever apply B+ until the tubes have finished the preconditioning period.
However once that is done you can apply B+ right away.Â
I've yet to see a GE that was trustworthy- I'm guessing that was not a 'G' but a 'GA' in the bantam envelope. GA's of any brand simply can't be used- they grid heatsink is tiny relative to the G variety and so the grid easily warps due to overheating.
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Old thread but if I may resurrect this.
Conditioning some RCA 6AS7G
1st Ralph (as always) he is right there is a lot of trouble to go with the American power output tubes on his amps, the Russian power tubes just work I have never seen a Svetlana arcing, already seen in the last 2 days 4 rcas arcing.
Can't comment on SQ yet but preliminar testing sounds to my ears in my system very close Russian vs American, kind of a Rocky IV
Currently cooking 28 rcas.
Question
If the tube was arcing with B+, does the conditioning process could remove after 4 days the arcing? Or once the tube arcs will always do? One GE specifically arced heavily to the point it smoked.
After 96 hours on standby do you apply B+ or do you shutdown, apply standby and then b+?
Honestly I just want to finish this batch testing, I am dying to put the Svetlana right in but don't want to let this opportunity pass specially if I have the American power tubes.
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I would like to know if anyone has compared the Sovteck to the RCA 6AS7G's and what their finding were? Sure- in our circuits the American tube makes more power and is less reliable. This is particularly true of the GA variant which should be avoided entirely due to being particularly unreliable. This is no small amount partially due to the fact that we employ a fixed bias scheme rather than self-bias. The American RCA is not spec'ced for fixed bias operation while the Russian (and Chinese) tubes seem to have no problem with this. But we have also found that the American tubes hog current more easily (which is why we suggest that they only be used in our gear if that gear is a MkIII series or later). In addition, the GA variant has a smaller grid heatsink, and since we employ Class A2 operation (where grid current can flow during part of the AC waveform at full power) the grid of such tubes can warp easily and cause an arc. So we recommend if you want the best reliability, to use the Russian power tubes. |
amp, I love Audio Valve equipment, they're well built and Helmut Becker was way ahead of his time with the ABR system. Great amps and preamps |
I would like to know if anyone has compared the Sovteck to the RCA 6AS7G's and what their finding were? |
I have used Sovtek and some other unknown brand of 6AS7Gs in a pair of AudioValve Baldur 70s for a number of years without trouble. I only recently discovered that they are/ have been made by RCA as well and was considering giving them a try. I was going to get them from Tube Depot/Tube Shop. |
ALSO ATMASPHERE EQUIPTMENT IS AWSOME!! |
Just to throw my two cents in and since I started the thread: regarding input tubes , in my atmasphere ma 2 3.3 amps RCA 6sn7 input tubes sound the best to me. I also have a set of silvania 6sn7's. RCA's seem to add a great warmth and smooth vocals ( like wow vocals) , to me the silvania's sound thin in a bad way, sound stage is not as forward also. So there is no doubt that anyone would hear the differences in sound of different nos input tubes, so input tubes do make a real difference.
Even more inportant and able to modify the sound are the tubes in the mp1 preamp. Again I prefer RCA.
The one exception is in the 1st position in the amps I was lucky enough to find a pair of kenrad jan vt 231 black bottle, that are quiet and not microphonic, this one pair of tubes adds the necessary bass to round out my amps with either set of tubes. |
Hi Ralph,
I thought they were talking about driver tubes. |
Sabai, you may be confusing the driver tubes (6SN7s) with the power tubes (6AS7G). I've been doing this a long time- I don't know if I have ever even heard of Mullard 6AS7Gs. |
I am using Mullards, Sylvanias and Tung Sols. The difference is night and day. |
I'm a new Atmasphere dealer but of the 3 x S30 amps and 2 x M60 amps I've sold I now only use a Russian 6H13C tube with the best sonic results and no arching. As Ralph states preconditioning really helps. On the side of the tube etched in a box on the glass it has the following:
BbInyCK
V1 - 823 r.
I bought over 200 in original NOS boxes but unfortunately I've sold all and my source in Russia is trying to procure more. If you can find these they are worth the asking price and in quantities are no more expensive than the 6AS7G tubes.
Good hunting
(Dealer disclaimer) |
So Sabi what brand tube did you purchase. Description of difference between nos and russian new stock, would be appreciated. Are nos 6as7g tubes possible noisy. |
Toothman,
Regarding output tubes for the S-30 I disagree, with all due respect. I spend 6 months sourcing tubes for the S-30 and the difference is night and day vs. the stock tubes. |
That should have been: The output tubes would NOT really change the sound. |
called Ralph at atmasphere again, he said that the output tubes would really change the sound. He recommended the Russian 6as7g output tubes. He also recommended turning the amps on stand by for 3 days as mentioned above, which can sometimes double the tube life. |
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. Atmasphere, this is very interesting. All is not just 6as7g variant but ALL power tubes. If you apply B+ during that period the preconditioning process is ended. I assume this is not done during tube testing/matching? |
Morgan Jones, he of "Valve amplifiers" fame, has written a piece on baking tubes that might be of use here. It's a variant on what Atmasphere talks about above, but using an oven to speed up the process of activating the getter flashing to absorb residual gas. Reductions in grid current are measured and found to be quite substantial, so long as you take care not to damage valves with phenolic bases. Morgan Jones, Baking Valves |
If you want nice 6SN7s, we have gotten really good feedback on the Psvanes, Sophias and TJ Music tubes. This applies to the amps and the preamps. |
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. |
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. |
I have the S-30. NOS tubes are essential, as they are for my Audio Horizons preamp. Finding the best tubes can take time and money. But once you do there is no going back. |
