Atma-Sphere MA-1 tube rolling

ralph, any theories or thoughts as to why this is the case?

We suspect that the environmental control is poor- tubes are made by hand and we've heard that they don't use Latex gloves in their assembly. That comes from Eric Barbour back when he was involved with the US Svetlana brand and so may well be completely inaccurate at this point but we see the same problems now that we saw 20 years go when he was there. That's my best guess as this would affect small signal tubes more. A pragmatic individual will simply roll with the punches...

But it sounds like I should stay away from Russian 6SN7's, which would include National, and some modern Tung Sol from Russia?

I can't speak to the National brand- some of that might be production prior to the fall of the Soviet empire and might actually be OK (Russian 6SN7s from the 1960s can be excellent, but pricey and the differences in appearance from the current Sovtek junk is subtle so buyer beware). But IMO the EH, Mullard or TungSol (which are all nearly the same thing) don't hold up to the (advertising) hype.

FWIW though we have seen some of the Gold Lion branded 12AU7s out of Russia be quite good.

For those who are interested, here is the link to another site, where tube rolling the 6SN7 voltage gain / driver tubes is discussed, as well as Ralph's input:

Atma-Sphere MA-2 Amplifier | What's Best Audio and Video Forum. The Best High End Audio Forum on the planet! (whatsbestforum.com)

• Mar 19, 2019

• #9

Doc nowack said:I’m roiling tubes to fleshout the lower mids and bass. I would be interested in hearing from others concerning there experience with tubes and placement in the amps.

The four tubes in the rear are the voltage amplifier tubes- the two 6SN7s closest to the front panel are the driver tubes.

So the driver tubes, if you want to try rolling, should have -GTA or -GTB suffixes as they are subjected to higher voltages which will shorten the life of a GT.

The voltage amplifier tubes are the most important to the sound of the amp. The voltage amplifier is where all the gain of the amp occurs. It is a differential cascode circuit aided by a constant current source, resulting in fairly high CMRR (Common Mode Rejection Ratio) over 100dB.

There are three 6SN7s in a differential and parallel arrangement which drive the cathodes of the 4th 6SN7 which is the top of the differential cascode. So those first three tubes have the most sonic impact. Yyou don't have to replace all three when auditioning a tube brand (although the cumulative effects will be easier to hear if you replace all three). The top of the cascode IOW has less effect on the overall sound than the bottom, so you replace the first three 6SN7s from the rear panel first, then the 4th.

We've got very good reports of the Psvane and TJ Music 6SN7 variants. Note that they should not be used in the 5th and 6th locations as they don't have the additional voltage rating of the -GTA and -GTB suffix. People report that these tubes have all the best character of the best NOS tubes (Ken Rad being the best, followed by the metal base chrome dome Sylvania after that probably the RCA red base or CBS Zalytron)) without any of the weaknesses! Pretty powerful statements IME.

On tip: have fun- don't drive yourself crazy. I go for a good musical presentation; if I'm getting that I spend the rest of the vintage tube money on more LPs

One more troubleshooting note: I had an awful buzzing/loud humming coming out of one of my Sound Lab speakers. I switched MA-1 monoblocks, and the buzzing switched to the other speaker. Then I proceeded to replace all the output tubes, first seven on one side, then seven on the other, and tested after each replacement. The buzzing was still there. Next, I proceeded to replace the most posterior (sonically important) driver/gain 6SN7 tubes, but the buzzing was still there. Lastly (almost) I replaced the main driver tube, which is in front in the Mk 3.3 model, and the buzzing immediately stopped. I was most surprised that this was the failed tube, as it was a new tube, with less than 30 hours on it, and it was a modern Tung Sol 6SN7 GTB. . . so it appears that currently Ralph’s suggestion to stay away from the Russian 6SN7’s seems to be rather accurate.

I was most surprised that this was the failed tube, as it was a new tube, with less than 30 hours on it, and it was a modern Tung Sol 6SN7 GTB. . . so it appears that currently Ralph’s suggestion to stay away from the Russian 6SN7’s seems to be rather accurate.

If you look on our website you'll find this warning, which has been there for nearly 20 years now

NOTE REGARDING SOME TUBES
We have seen on-going problems with 6SN7s marked as "Sovtek" and "Electro Harmonics" More recently we have seen similar problems in reissue tubes marked "Tung Sol" and "Mullard". We do not recommend these tubes in our products. While they will not damage our products, neither will they perform optimally or reliably. If you are experiencing a problem and any of these tubes are installed, replace them first before doing anything else.

@atmasphere:
Thanks for the reply.  I must admit, I haven't read much of your website, but only the instruction manual that came with the MA-1.  
The amplifiers are a phenomenal match for the Sound Labs.  I'm enjoying them immensely.  Thanks for your great work!