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Atma-sphere amps best power tubes

This question has been debated before on A-gon but without a clear onclusion. I wonder, is it worth it, to upgrade from stock Russian or China output tubes (6as7g), to American NOS tubes?

It seems that everyone agrees that upgrading the Atma-sphere driver tubes from stock Russian/Chinese to NOS is well worth it. This is my experience also.

I am wondering about changing the output / power tubes too. I wonder if a change to NOS is well worth it also in the output case.

It seems likely, judging from my other equipment testing.

My Audiotailor Jade OTL headphone amp uses 1 6asg7 and 1 12ax7. No surprise - it sounds better with a good NOS 12ax7 compared to Russian/Chinese stock 12ax7.

More surprisingly, it also sounds clearly better with a NOS 6as7g output tube (General Electric US NOS). The improvement is largest with the driver tube but not so much behind with the output tube. Almost 50 50.

A lot of output tubes are involved - 28 tubes in my MA-1 amps. Changing them all is costly, and so I would like to know some user experience before I go into this.
o_holter
mechans
2,999 posts
 
Well it's ten days later, has the perceived lack of overall volume and slam come back? Curious myself because I have a headphone amp that can use 6AS7Gs . Right now I am happiest with 5998s in there (so called "Domino" plates). I have use 6080s and preferred the RCAs. I had some 6AS7G variants but no RCA or other U.S. tubes.
c1ferrari
464 posts
 
O-holter,

Are you still using Sylvanias and RCA's in the 6SN7 positions of your MA-1's?

-Sam
o_holter OP
541 posts
 
I am away travelling and also have some speaker driver problems (not tube-related) so it will take some time before I can answer these questions.
o_holter OP
541 posts
 
Finally I've had time to test my 28 6AS7G output tubes and about 20 extras, in my new Beck RM-1 tester. The measurements vary a lot (between tubes, and internally between sections) - all in all, quite disappointing, both for the RCA NOS set and my new stock russian (mostly Svetlana). 2 of the RCA tubes had one section dead, and 2 measured VERY low. No wonder I lacked some volume and slam. I have now changed these 4 into four extra RCA's that I bought, knowing that this was likely to happen. I actually bought 6 extras, but 2 of them were bad. It seems typical, regarding this tube.

I have also changed the driver tubes, taking out two Sylvanias that may have been problematic / worn out. On the mk 2.2 long chassis amps, the positions are not very intuitive, so perhaps other users may find the following information useful (checked with Ralph).

Position - tube type - function

v4 (front corner facing output tubes) – 6SN7GTA or 6SN7GTB – output section driver

v2 – 6SN7GT - sections should be matched – top half of the cascode voltage

v1 – 6BX7 (or 6BL7) - sections should be matched – bottom half of the cascode voltage

v3 (back corner facing power) - 6SN7GT - constant current source.

I now mainly use new tubes from Atma-Sphere that I got in 2013. They were hard-sounding compared to the NOS Sylvania I was used to, and I disliked them at first. Gradually they became, well, more acceptable. I use the A-S supplied General Electric 6BX7 in the v1 position. I keep a Sylvania in the v2 position, but use the the new Chinese brown-base 6SN7GT in v4 and v1.
mechans
2,999 posts
 
O_Holter, Interesting report. The truth can be painful. I have been a tube hoarder after discovering that changing out the Chinese 6SN7 driver for NOS Sylvania GTBs (not even fancy pants tubes)in my first tube amp made such a positive impact on the sound. That was about 12 or more years ago. Now divorced I have my tube collection but few places to use it.
I have about 75 really good, some quite rare, 6SN7s in arms length at the moment-Feel free to contact me, if the rules allow it.
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