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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.
Ag insider logo xs@2xo_holter
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o_holter OP
978 posts
 
I read somewhere that testing the 6AS7G is one thing - another is how it actually performs. (And - how it actually performs in an Atma amp).

I had the amps to repair recently and the repair man Hans Kise tested while I looked, finding that about 40 per cent of the 28 output tubes measured non-optimal. He had the amps lying on the side, bottom plate removed, and used a multimeter on the connections of each tube in the amp itself (not a tube tester). Two days later he was on his way to trash the non-optimal tubes when I told him to wait a little - he managed to salvage them, before the garbage collection. I want to test them some more.
acresverde
400 posts
 
I keep hoping that Ralph and crew will follow thru one day on the oft hinted at 6AS7G tube tester that they were going to build. A lot of us would really like to put to bed once and for all the issue of whether or not our various testers are up to the task of RELIABLY evaluating our power tubes or not. A purpose built unit would be a godsend.
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o_holter OP
978 posts
 
Hi Acresverde - I have bought a RM-1 tube tester from Beck Electronics in Germany, custom setup so it can test 6AS7G (among others). I have not received it yet, so we shall see, does it do the job. My impression, living with 28 of these tubes for some years, plus reading others' experience, is that they are unpredictable. It seems that it is not so easy to tell if a tube will arc or not. I have had "tested" sets of 28 tubes, yet with quite a few failures, here also.
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o_holter OP
978 posts
 
Burning in a set of 28 RCA 6AS7Gs right now - following Atma-sphere advice, 72 hours on Standby, before turning the amps On. I hope they work OK, and give the same sonic improvement that I have heard other places, changing from stock Chinese/Russian versions.
rushton's avatar
rushton
2,445 posts
 
Will be very interested to hear you assessment of the sound quality, O_holter.
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