Driver board options

I'm currently using the low gain 12AU7 board with a 6SN7, with adapter, in the gain position. I really like how it sounds with this configuration. I tried using 12BH7's in the phase positions, but I really did not care for the sound of that combo.

Now here's the question.

I would like to replace the driver board because I did "abuse it" tweaking and trying different things. So now it's time to decide if I go with the 12AU7 or 6SN7 version. My only concern is that I didn't prefer the 12BH7's as phase tubes and I'm concerned that I may not prefer the 6SN7's as phase tubes.

How do others feel about using the straight 3 6SN7 version, vs a 12AU7 phase tube with 6SN7 gain tube.

thanks

Hello Telescope12,

I read your post, but I held off responding, hoping someone who had actually tried both the noval and octal board would respond, because I was curious too. Since no one has, I'm going to post my opinion and experience.

Like you, I'm now using an adapter in the 12AU7 driver socket, allowing me to use a 6SN7, something I tried starting in August of 2021. I'm not normally given to hyperbole, but the improvement over the 12AU7 in my VTA circuit was "day and night". I'll be honest, I never liked the sound of my ST-70 after installing the VTA board. I tried a few different NOS 12AU7s, EH 12BH7s, changed coupling caps, and even a few key resistors, but the sound was still not to my liking. After reading yet another post on other audio forums about the non-linearity of the 12AU7 tube, I decided to order the adapter and try a 6SN7 in my VTA. To say I'm happy is an understatement. i finally have an amp I can enjoy listening to music with.

Prior to posting my reply, I did a search of the VTA forum this morning, and found this: https://dynacotubeaudio.forumotion.com/t3361-octal-driver-for-m125?highlight=octal

Scroll down to Roy's reply, where he says, "90% of my customers who have upgraded their amps with the octal board say it sounds better."

Further down in his reply, Roy says, "For anyone who wants to invest $40-50 in a tube and a socket adapter, buy a 6SN7 to 12AU7 socket adapter and a 6SN7, and report back to me . . ."

I'm reporting back, albeit nearly five years late (I only found Roy's post this morning), but to my ears, the differences aren't at all subtle. I've put a 12AU7 and 12BH7 back in the driver position in place of the 6SN7, but quickly went back to the 6SN7 (either NOS GE 6SN7GTB or new production Tung-Sol) and my musical enjoyment returned.

If I were in your position, and decided that my board was damaged and required replacement, I'd have no hesitation saying I'd be ordering the octal board from Roy.

AMEN to the 6SN7 as a driver tube, and as a phase splitter . . . well, the phase splitter doesn't have a huge influence on the sound like the center gain tube does,
but everyone knows (well, almost everyone) that the 6SN7 is THE golden ear audio tube.

So If I wanted to try the 6SN7, what kind of adaptor would I need and who sells a good one?

hundreds on them on ebay but most all from China,
TubeDepot.com sells them and you can get from them in a few days

Hops wrote:So If I wanted to try the 6SN7, what kind of adaptor would I need and who sells a good one?

If you have the most common VTA board configured for 12AU7s, you would need a 6SN7 (8-pin tube) to 12AU7 (9-pin socket) adapter. Here's the one I bought:

https://www.ebay.com/itm/193442642368

...but as both Bob and Roy mentioned, there are many to choose from on ebay. I just picked a seller with good feedback, one offering an adapter without an exposed circuit board, and ordered it. The seller contacted me after placing my order to confirm that my filament requirements were 6.3 V, which of course the VTA circuit is. You asked about a "good one", and I have no complaints about the quality of the one I received, although it's the only one I've tried.

Ever suspicious about Chinese quality control, I mapped out a pin continuity test from the data sheets of the two tubes (as shown below) prior to using the adapter in my VTA. The adapter I got was configured correctly.

12AU7 socket to 6SN7 tube adapter

12AU7 pin #1  = 6SN7 pin #2  (2nd plate)
#2         =             #1 (2nd grid)
#3         =             #3 (2nd cathode)
#4 and #5  =        #7 (heater)
#6          =            #5 (1st plate)
#7          =            #4 (1st grid)    
#8          =            #6  (1st cathode)    
#9          =            #8 (heater)

Thanks 1973shovel. I ordered a pair of adaptors from your link.

I'm intrigued by this and am considering trying the adapters as my current drivers have gotten a bit noisy.

What 6SN7 tubes have people tried and liked?

Hops wrote:Thanks 1973shovel.    I ordered a pair of adaptors from your link.  

You're welcome, Hops. I hope you get results as pleasing as I did using the 6SN7 as a driver tube. Please post your results when you've tried the 6SN7 to let us know.

vtshopdog wrote:What 6SN7 tubes have people tried and liked?

I've only tried two so far, a NOS GE 6SN7GTB with a 1956 date code, and a new production Tung-Sol 6SN7GTB, purchased from Jim McShane. I only have about three hours on the GE, but so far it sounds very nice. The Tung-Sol was a bit bright when I first installed it, but it settled down after maybe ten hours, and I'm very happy with it too.

And speaking of Jim McShane, when I ordered the Tung-Sol, Jim informed me that sometimes (in general) adapters can roll off the highs slightly, due to some of them adding a bit of capacitance to the circuit. I didn't notice any diminished top-end with the adapter, but I may have been so wowed by the sound over a 12AU7 or 12BH7 that I didn't notice. Roy's octal board would eliminate any concerns about an adapter, and now that I know how much improvement a 6SN7 offers, I may eventually order a new octal board at some point in the future.

Below is a link to four pages of 6SN7 comments here on the VTA forum, found using the "search" feature. One tube I've been tempted by, based on recommendations on various audio forums, is the Shuguang CV-181-Z, with some saying it's as good as any NOS 6SN7 they've ever tried. If it wasn't so damn expensive, coupled with my distrust of the quality of Chinese tubes, I'd order one. While I've read many "it sounds great" comments, I've also read of premature failures, saying given the cost of postage to China, that it wasn't worth sending back. So far I've been unwilling to invest $80 "just to see", but then I've never been much of a gambler.

https://dynacotubeaudio.forumotion.com/t2715-what-s-your-favourite-6sn7-tube?highlight=6SN7

When I ordered my adapter it did take 4 weeks to arrive. So do consider that.

How many of you use 12BH7 tubes in the phase positions? I was using them when I wasn't using an adapter. Now that I have the adapter, I find that I no longer prefer the 12BH7 in the phase positions.

The 12BH7 is a more linear tube, so again, I'm wondering if using the 6SN7, a more linear tube, is going to have a similar result?

I have the ST-120 and have the lower gain 12au7 board. Sometimes use an adapter and have found the cheap Chinese adapters have a tendency to be noisy and do not give a person much confidence to use them. So I searched the forums and found on headfi they recommended Garage1217 which makes tube headphone kit amps, so I ordered one and was very happy with the construction and it is about $25.

I have listed the website below, no affiliation and I have not purchased anything from them but this 6SN7 to 12AU7 adapter. There are a few versions make sure you get I believe the 2nd one that says center tap at 6.3 volts. I highly recommend this adapter!!

BTW you should give the Mazda 12au7 late 1950, or early 1960, a try might change your mind about this tube.


http://www.garage1217.com/g1217_011.htm

Well that all sounds great but what if you have the original power transformer Doesn't that tube require an upgraded transformer with the additional current draw?

Tubey1 and all
the original 60 year old Dynaco ST70 used two 7199 tubes as drivers, and they used a total of 900ma of filament current (plus 6A for the four EL34 output tubes).
Our VTA70 driver board with three 12AU7 tubes uses a total of 900ma of filament current, same amount.
The old amp was also designed with two preamp power sockets on the front of the amp, which we now use a test points to check the tube bias.
Those had enough current from the transformer for an additional 1000ma of current, or 1900ma total.
The octal driver board uses twice the filament power of the original or our replacement, three 6SN7s use 1800ma total filament current.
Just under the rating of the original 60 year old amp.
But as most users already know, those old 50-60 year old power transformers run pretty hot, even just running two or three small tubes.
So we've always recommended buying a newer transformer (any replacements made in the past 20 years are usually rated 6v 5A x 2 instead of the original 6v 4A x 2
(those same windings also power the output tubes, EL34s use 1.5A each, or 6A total) so the new transformers have way more reserve and even if you use
four KT88 output tubes total 8A and three 6SN7 drivers total 1.8A you are not exceeding their rating.

Thank you for the detailed explanation - good to know!!