VAC Signature MK2a pre "phono tube questions"

Hi Dev,

The phono circuit in your preamp is the same as in the Phi Beta, which I'll receive on Friday. I, too, asked Brent about rolling the 12AX7s a few weeks ago and received similar info. One thing I'll add is that he said the back row, the inputs, play the greatest roll in sonics--back to front, in order of decreasing influence. The front pair, under the most stress, have the least influence on sonics and will have the shortest lifespan. He said to place the tubes you care about the least in that position. I'll probably start the rolling process by leaving the Chinese tubes there and placing my fav 1964 USA Amperex 7308 into the back because they have such great focus, resolution, and balance. Then I'll see what middle pair is best for tone. But, of course, I'll ultimately experiment with all positions

Hey Jafox,

I believe Dev asked his question because of this thread that was started just a few days ago.

VAC Thread from 9-5-11

Most of the respondents all seem to have stated that using NOS tubes were no better than the stock tubes that come with the VAC equipment.

(Interesting responses that went against my instincts as well. I find that using NOS tubes in my Lamm hybrid amps yields small, yet significant, improvements in the sound quality. However, I don't own VAC equipment, (although I wish I did!), so I don't know for sure that using NOS is the way to go.)

My two cents worth.

Hi Wrm57,

Congrats! and thanks for that added info., what you wrote in relation to position really provides clarification of such and greatly appreciated. I assumed such but this now confirms.

Hi Kurt tank,

ya I read that thread also but no one really appeared to be specific in relation to the phono stage only tubes and now that we have this info. we know and such will assist with any others interested.

Next will be the actual comparisons and in the end the findings, unfortuantely mine will have to wait a bit because my amps are still in break-in mode and I don't want to miss out on hearing any sonic differences due to such.

I have some very nice matched paires from different manufactures on hand and will most defiantly be trying and comparing, hopefully Wrm57 will report back his findings.

Hey if it works out the stock tubes work than that will be a bonus but I would be shocked just because of my past experience with other gear doing such, time will tell.

Wrm57

I'll probably start the rolling process by leaving the Chinese tubes there and placing my fav 1964 USA Amperex 7308 into the back

Unless you have specific confirmation from Kevin or Brent, I'd think twice before putting an NOS 6DJ8/6922/7308 into a slot designated for a 12AX7. They are both 9 pin miniature dual triodes but unless the circuits are specifically designed for it, they are not direct substitutes by any means. I realize that Randy White and Dan Wright and some others have circuits into which they can be subbed, but I do not remember reading anything that indicates that that is the case w the Ren pre-amps (great unit, BTW.)

D'oh! I meant medical grade Amperex 12AX7. I mentally misfired because I had VAC install a 6922 switch for the 8416 tubes (at their recommendation) in the linestage and was thinking the tubes I'll use to roll that position. No, I'd never put a 7308 into the 12AX7 socket. :) Thanks for catching it.