Atma-Sphere MA-1 tube rolling

I've had my MP-1 and M60s for 20 years now. Follow Ralph's advice and stick with the Russian provenance 6AS7Gs or, alternatively, the 6H13C. I had a brief fling with the Chinese variant and found they had a high failure rate/short life span.

IME, it was problematic to roll the 6AS7 output tubes in my M-60.
I have always been a fan of NOS,
I got a set of 6AS7Gs from Brent Jesse.
They we’re not matched and were three different brands as Brent said.
As Ralph said, the failure rate of NOS is high compared to the stock Russian. 3 of the 16 failed. However, when I got good ones in, the power output went up about 20% and the tone was much better.
I would highly recommend going with NOS as long as you are aware of the failure rate,

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.