Atma-sphere amps best power tubes

O-holter,

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

-Sam

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.

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.

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.

Here is an update on my RCA and other US NOS output tubes, over the last year. No problems at all - they all run fine. Adding to better sound. I am glad that I followed the careful break in procedure, described by Atma-sphere.
Ø