OTL Asylum

OTL, Output Transformerless Amplifier User Group.

Return to OTL Asylum


Message Sort: Post Order or Asylum Reverse Threaded

NOS AS7s in MA-1s?

67.174.219.72

Posted on July 23, 2021 at 11:38:07
ACHiPo
Audiophile

Posts: 62
Location: California
Joined: March 26, 2016
Contributor
  Since:
June 23, 2021
This last retubing I put NOS AS7s in the front four positions of my M60s. I saw this recommended somewhere, and I like the look. I can't tell any sonic differences, but the GE JAN NOS tubes supposedly have a little more power than the Sinos.

Does it make sense to use the GE JAN NOS tubes in the MA-1s? If so, should I run all 28 the same, or mix/match with Sino tubes? If mix/match, which locations should the NOS tubes go in?

 

Hide full thread outline!
    ...
RE: NOS AS7s in MA-1s?, posted on July 23, 2021 at 11:38:47
ACHiPo
Audiophile

Posts: 62
Location: California
Joined: March 26, 2016
Contributor
  Since:
June 23, 2021
Subscribed

 

RE: NOS AS7s in MA-1s?, posted on July 27, 2021 at 10:31:05
ACHiPo
Audiophile

Posts: 62
Location: California
Joined: March 26, 2016
Contributor
  Since:
June 23, 2021
No input or recommendations?

 

RE: NOS AS7s in MA-1s?, posted on July 28, 2021 at 15:53:38
voolston
Audiophile

Posts: 3073
Location: New Orleans
Joined: October 14, 1999
This subject has been well addressed before and the simple answer is that you will not likely get a recommendation for anything but the Russian Sovteks and the Chinese Sinos that Ralph recommends for his amps. There's really nothing else to use so these amps just don't lend themselves to tube rolling, as far as the power tubes are concerned anyways. In the thread below, acres verde mentioned reliability issues with the Chinese output tubes, so there's one recommendation to stick with the Sovteks.

That said, if you are using other tubes that work, won't hurt the amp, and you like the sound of, then go for it. As far as mixing and matching, I would distribute them evenly between the two "sides" of the amp. With the original chassis, each "side" is made up of a row of 7 tubes.

I recently numbered all of my tubes (including spares), measured each triode, entered the data on a spreadsheet, and sorted the data so that I could as best as humanly possible, evenly distribute my best tubes between the amps and then between the two rows within each amp. This way each of the four total rows essentially have, as close as possible, the same collective value. Did I hear any change by doing this? Nope, but I still feel good about it :-)

voolston - audiophile by day, music lover by night

 

RE: NOS AS7s in MA-1s?, posted on July 28, 2021 at 15:59:04
ACHiPo
Audiophile

Posts: 62
Location: California
Joined: March 26, 2016
Contributor
  Since:
June 23, 2021
Vooston,
Thank you. That is the information I was looking for. I'll stick to the still-affordable Sino power tubes. The Russian Sovteks have gotten crazy expensive.

Oh, and hats off to your OCD. I actually thought about the same approach, only rather than a spreadsheet I figured I'd use a silver Sharpie on the base. I don't have a tube tester, but it's easy to get confused even with the M60's 8 tubes let alone the 14 of the MA1s.
Evan

 

RE: NOS AS7s in MA-1s?, posted on July 29, 2021 at 06:57:20
voolston
Audiophile

Posts: 3073
Location: New Orleans
Joined: October 14, 1999
A silver sharpie would work fine if you want to number the tubes and maintain some kind of log. I put little pieces of masking tape on the tube bases to write numbers on, but was careful to put them on the "back" side so I don't have to see them as my OCD side would not like that! I did recently find that I had about five dead tubes in one monoblock and never knew it by listening, so I wouldn't stress too much about matching. I just went through the effort out of principle (and because I had access to a tube tester). I understand one way to know if something off is to simply check the dc offset and bias. If the previously set values are off, then likely there is a weak or dead tube to blame. As acres verde also mentioned, whenever there is a problem, it is ALWAYS a tube issue.

voolston - audiophile by day, music lover by night

 

Be careful of American 6AS7s, posted on August 9, 2021 at 12:20:10
Ralph
Manufacturer

Posts: 4245
Location: Minnesota
Joined: April 24, 2002
The 6AS7G is the only version worthy of experimentation IMO/IME. With any other type (6080 or 6AS7GA) I think you'll find reliability to really be a problem.

Even with the American 6AS7Gs, I recommend preconditioning for at least 4 days and 4 nights at a minimum. This helps reduce arcing issues, especially right after setup.

No amount of preconditioning will help a 6AS7GA. The 'A' version has a smaller heatsink for the control grid, which warps and arcs in the class A2 region in which we operate the power tubes.

As a general rule of thumb, if the tube does not have the ST-7 envelope (the taller 'Coke bottle' package) then it won't have the grid heatsink needed and will likely be failure prone.

We've done alright with the Chinese tubes but they too need about 4 days and nights of preconditioning. They have certain failure modes that the Russian 6H13C does not. So the Russian tube is the preferred tube insofar as reliability is concerned.

 

RE: Be careful of American 6AS7s, posted on August 9, 2021 at 12:33:11
ACHiPo
Audiophile

Posts: 62
Location: California
Joined: March 26, 2016
Contributor
  Since:
June 23, 2021
Ralph,
Thank you. Once again I realize how little I know about this stuff. Humbling. I guess each letter and number means something, at least between a G and a GA!
Evan

 

Page processed in 0.027 seconds.