Atma-Sphere MA-1 tube rolling

I know that old stock 6AS7Gs dont typically work as well in place of the newer types that Ralph sells. The same may be true of 6080s. 

My advice would be to concentrate on the 6SN7s and to leave the power tubes alone at least for now. Not all sections are equal in terms of sonic impact and it may be that you need a pair of GTA or GTB in one section with GTs/5692s being acceptable elsewhere.  Call Ralph and he will clear this up. 

I have retubed Atma-spheres before and my clients have reported positive results using old stock 6SN7s. I have never replaced any power tubes. Mixing 6SN7 pairs with different strengths seems to yield positive results. 

@drbond
My advice is to stay away from the 6080s on these amps! They are not built to the same spec as 6AS7Gs. The 6080 typically has a smaller grid heatsink and since the amp is biased in class A2, the grid can warp at higher power levels, causing the tube to arc- and often taking out multiple tubes at the same time. This won't damage the amp or speaker, but it can result in the user getting gun-shy and thinking there's something wrong with the amp when there isn't!  Some people claim to have had good luck with 6080s but IME they've told me that while dealing in the same breath with failing tubes. 


This advice extends to the 6AS7GA as well as any other variants. Stick to the 6AS7G. Now when dealing with American versions, if the tubes are NOS they will need to be preconditioned for *at least* 4 days and 4 nights in order to have any reliability. Otherwise the cathode coatings flake off and cause the tube to arc and fail. Of all the vintage types the Sylvania made examples hold up the best (and not surprisingly are the hardest to find).


So the Russian '6H13C' is the most reliable IME. If you use the Chinese 6N13 make sure its a military example such as seen with the 'PJ' suffix. The Chinese tube can develop what looks like a smoke ring on the inside of the glass; if you see this discard the tube (because the tube is failing and might arc). The Russian tube does not do that.

always nice to hear advice from the actual maker of nice gear... 

@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.

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.