Atma-Sphere MA-1 tube rolling

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?

Actually the stock tubes **are** either the Russian or Chinese tube (which seem to sound the same; the difference is in how they fail).

Would you suggest just rolling the 6SN7 driver tubes for more adjustability? 

People roll the 6SN7s all the time with nice results. We've found that that Sophia tubes while sounding great at first, seem to have a short life of maybe only 6 months, whereas a regular NOS tube in the same spot can go for years. The one tricky bit is the driver tube which in the MA-1 will be in a different location depending on when the MA-1 was built. If you have a version with reflected left and right hand chassis the driver tube is on the corner facing the power tubes; if a newer chassis the driver tube is the one in the front. This particular tube must have a -GTA or -GTB suffix if you're using an NOS type. Modern 6SN7s like the Shugang 6SN7 or Sovtek are marked 'GT' but are actually GTBs.


If you are forced to use Russian made 6SN7s (which conversely and confusingly from the Russian power tubes are usually a poor choice), they should be screened on a tube tester to show no leakage at all on the leakage test, otherwise you may encounter a buzz. The lifespan of these tubes is also really variable going anywhere from 2 weeks (in which case send it back to where you got it and get it replaced; most tube sellers have a 90 day warranty) to maybe 2 years.

i too have wondered why russian power tubes are very good (i use el34 and kt88 variants), yet the sound of russian low level tubes like 6922 6sl7/sn7 are rather poor (lacking midrange bloom) and russian rectifiers like gz34's are abysmal in quality and lifespan

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

@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. 

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