2. amps-preamps
  3. 183518-179778

Tubes for a pre stage... matched NEW or unmatched identical NOS?

I have this question for so long:

On a integrated amplifier that uses a pair of 12au7 tubes (or alternatives) on the preamp section (Rogue Sphinx, for example) what is best option:
a) to have an unmached unbalanced pair of identical NOS tubes
b) to have of matched balanced pair of modern tubes
c) to have balanced 12au7 tubes no matter if they are matching

Once asked JJ why they didn’t offer matched 12au7 type of tubes and the answer was the it is irrelevant for the kind of use they are intended in audio circuitry. Is this right?

My question only makes sense when forced to keep tube-rolling costs down (or tube substitution when the stock ones fail) because the obvious and better choice is matched NOS, like those from Amperex or Mullard.

audiofilo123
ieales's avatar
ieales
1,201 posts
 

What are your favorite 12au7 type NEW production?

What amp? What purpose? What circuit? What music? What room? What system?

ALL sound different in different places. The validity of most opinions is ZERO.

And after how many hours as they change from first turn on...

jjss49's avatar
Ag insider logo xs@2x
jjss49
6,612 posts
 

people posting seem to be getting confused, referring to 6dj8 tube variants and such, when the op is specifically asking about 12au7 tubes and their equivalents

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets - no need to play with the relatively grim and unreliable chinese and russian current production when so many nice old stock ones are around

having said this, the 6dj8 types -- especially higher end dutch or uk cca ecc188 variants, what have you, that is a different universe, an entirely different discussion about value, availabilty and affordability

brownred6
17 posts
 

I’ve got a good assortment of these nos premium 12au7’s and 12ax7’s so I match them up as accurately as I can with my Hickok tester and use them that way. I really hear the difference in brand and era but not positive the matching is so critical but most experts would probably do what I do given the choice that I’ve accumulated 

thecarpathian
4,185 posts
 

An inexpensive nos 12au7 type will almost always sound better than a new production tube of the same price. An expensive tube like an Amperex 7316, no contest. Look for reasonably priced nos. You'll be glad you did.

ieales's avatar
ieales
1,201 posts
 

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets 

The problem is what is 'well matched'? At the datasheet params? NONE of my tubes operate anywhere near them.

I've bought plenty of NOS 'matched' 12AU7 & commercial variants. NOT one came close to the claimed Gm when operated at the amplifier parameters. NOR were the Gm matched at datasheet parameters. 

NOS tubes often have significant gas after ½c. on the shelf and need a while for the getter to clear it. Some advocate baking, but others say never. Induction heating may be the answer.

Expect any NOS tube to change significantly over the first number of hours.

Methinks Confirmation Bias accounts for a fair portion of NOS enthusiasm.

More to discover