It's the gain tube as I understand it

Posted by JoshT (A) on April 3, 2023 at 07:39:37

In Reply to: What does the middle 6NS7 do? posted by Rod M on April 2, 2023 at 19:41:34:

Here is what VTA says on their website about their "classic" ST-70 driver board:

"The upgraded VTA driver board uses three new 12AU7 or 12BH7 triodes in place of the two mediocre sounding 7199 pentode/triode tubes. Dynaco saved money using a two tube 7199 board design but made some serious compromises in sound quality." Chris who built my amp says much the same thing in his owner's manual.

Since then, VTA started offering a three tube octal driver board as an upgrade option.

And here is what inmate airtime said about the 12AU7 driver board when I first posted about buying the amp in February on the Amp Asylum:

"Because of its lack of linearity the 12AU7 should never be used as a gain tube. It sounds awful in that position and no amount of tube rolling is going to fix it. Designers are only using it because it quickly fixes a number of gain issues. The 6SN7 is the tube to use on that driver board."

Based on my actual listening, I don't agree that the 12AU& sounds awful in that position. Far from it. I do think the 6NS7 sounds better though.

As you can see on the linked page, VTA (tubes4hifi) still sell both as replacement parts and still seem to show the 12au7 board as being the standard approach, but Roy was clear when I emailed him that replacing the center tube with a 6NS7 and adapter should be an improvement.

But I have no idea how any of this would apply to the original two tube circuit.

___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

http://www.tubes4hifi.com/ST70.htm (Open in New Window)

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Follow Ups Full Thread

Topic - Follow-up on new build ST-70 with the 6NS7 tube - JoshT 09:14:38 04/01/23 (20)

Just read yesterday... - Cougar 11:33:25 04/03/23 (4)

RE: Just read yesterday... - 1973shovel 11:46:49 04/03/23 (3)

I'm happy with the 6H8C... - Cougar 13:42:43 04/03/23 (2)

I'll be looking forward to your assessment - 1973shovel 08:32:18 04/04/23 (1)

I will do that... - Cougar 11:39:16 04/04/23 (0)

ST 70 - M3 lover 10:31:02 04/03/23 (1)

RE: ST 70 - JoshT 13:49:29 04/03/23 (0)

"All of that said, I don't hate the 12AU7s" - 1973shovel 09:20:36 04/03/23 (0)

What does the middle 6NS7 do? - Rod M 19:41:34 04/02/23 (1)

It's the gain tube as I understand it - JoshT 07:39:37 04/03/23 (0)

RE: Follow-up on new build ST-70 with the 6NS7 tube - Sondek 07:48:12 04/02/23 (6)

A 6CG7 could be used... - 1973shovel 09:09:23 04/03/23 (4)

Would that be easier than just replacing the driver board with the VTA Octal one? - JoshT 09:14:27 04/03/23 (3)

It would certainly be "easier" from a physical labor standpoint - 1973shovel 09:53:40 04/03/23 (2)

Thanks - JoshT 13:43:13 04/03/23 (1)

I'm glad it's working out for you (nt) - 1973shovel 07:09:09 04/04/23 (0)

I dunno - hope others respond though! - JoshT 07:46:44 04/03/23 (0)

Glad to hear you are.... - Cougar 19:33:19 04/01/23 (1)

Thanks! nt - JoshT 07:47:09 04/03/23 (0)

RE: Follow-up on new build ST-70 with the 6NS7 tube - Triode_Kingdom 18:16:42 04/01/23 (0)

Follow Ups

It's the gain tube as I understand it - JoshT 07:39:37 04/03/23 (0)

It's the gain tube as I understand it

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