VAC Signature MK2a pre "phono tube questions"

Inna

Most manufacturers do not use because of cost and availability. Most manufactures buy new tubes by the case and sort them out from there usually from China or Russia.
I am sure most would love to supply nice NOS, but have you tried buying a nice matched pair of Telefunken 12AX7 lately, you will likely pay around $200 and up depending on vintage and type.

Also when you use the Chinese or Russian tubes you have a standard to work with, meaning customers will be able to find the same tubes now and not have to hunt for expensive NOS. So the sound is consistant with what the manufacuter has sold you.

All that being said nice NOS tubes are very good compared to most of what is available new today.

Hi Jafox,

You ask why I would ask such questions, why wouldn't I, you obviously did not know the answers to my question entirely either. I'm always learning, I also like to know what other owners specifically are using or what they have found in relation to comparisions. I'm a fairly new comer also to owning the VAC pre-amp specifically so I had no clue to what these tubes were responsible for. I have read info. in relation to the line stage tube changes and also some with the 300.1 amps but nothing directed to the actual phono section.

As for what tubes come with a specific pce is out of mine and your control and a debate in general which should be taken up and directed to the manufacture but I do agree with in general what Pcosta wrote.

My questions

I see no replies from actual owners as of yet but thanks for the general info.

I do have some info. that was provided by Brent;

- The back row of tubes are the inputs.
- Middle row second gain stage.
- Front row are the low impedance output buffers.

"They all play a part in the sound, but the front set are theoretically under the most stress, so I would avoid putting anything delicate and/or rare in that position."

"The Chineses 12AX7 is currently the best one on the market by far. They are of current manufacture, and remarkable in that regard, though they are from the top 10% of the batch in terms of performance, even before they are graded.
The Chinese tubes are not the prettiest tubes, but they are remarkably consistant."

"With 6 tubes to play with, simply swapping them around usually nets a good result in terms of channel balance, and with passive RIAA, they aren't as critcal to one another."

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.