Atma-Sphere MA-1 tube rolling

@atmasphere:
Thank you for your detailed response!  
Have your customers mentioned to you what changing out the stock 6AS7G tubes for either the Russian 6H13C or the Chinese (I assume ShuGuang) tubes do differently, for better or worse? 
Would you suggest just rolling the 6SN7 driver tubes for more adjustability?  
Thanks.

@atmasphere 
Thank you for the reply. 

In my estimation, your direct contact with the people who use your products, and your willingness to share your time and expertise, shows that you really enjoy what you do, and your products reflect that.  

I rolled out the non-driver Chinese 6SN7's, and placed Tung Sol NOS 6SN7GTB in their stead, and the sound stage and detail really materialized right in front of me.  

I'm planning on trying Ken-Rad VT231's and CBS Hytron 5692's in the primary positions of the 6SN7's closest to the back of the MA-1 mark 3.3 next.  But it sounds like I should stay away from Russian 6SN7's, which would include National, and some modern Tung Sol from Russia?  

I was considering trying out other power tubes (like possibly the 7236), but given your advice, I think I'll just stick to the Russian 6H13C. 

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.

@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! 

@crowdaddy2

Insofar as I know, the best way to find a failed tube is trial and error:  you should have a second full set on hand anyways.  If replacing all the tubes doesn't work, send back to manufacturer for check-up.  Ralph and Atma-Sphere will be glad to evaluate the problem.  I don't think anyone can really tell you what the problem is without physically evaluating the unit.  

Best wishes!