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6SN-7's

75.71.37.161
Posted on December 28, 2014 at 07:18:11
throwback
Audiophile

Posts: 762
Location: Colorado
Joined: December 8, 2003
 As I look at the front of my MA-1 monos (where the meters are)I see five 6SN-7 input tubes. Ralph told me once that they are ranked in order of importance, but I have forgotten which is which. So, a couple of questions for you guys.

1. Is the most important 6SN-7 on the end closest to the meter, or on the other end?

2. Is it worth doing some tube rolling to optimize this (or any other)6SN-7 in the string? What are the best tubes?

3. While I'm at it, let me confess that I am still using the stock feet. Is it possible to make an improvement by using different ones? What should I try?

Happy New Year to you all.

 

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RE: 6SN-7's, posted on December 28, 2014 at 20:30:21
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Hi Chuck, Happy New Year to you, too. Probably the best person to consult on which tube does what would be Ralph, since there are so many iterations of the MA1. Two of the tubes (and I do not know which two on your amplifier) comprise a dual-differential cascode input stage. Those would be the two most important tubes in terms of an effect on sonics. One of the other three is probably serving as a Constant Current Source for the dual-differential cascode. And the remaining two tubes are either both drivers for the array of output tubes, or only one is the driver tube and the other serves as a CCS for it.

You could in fact identify the two tubes that form the input stage (the dual-diff cascode) by flipping your amplifier over and removing the bottom plate. Then look to see which tube receives the wires from the XLR input jack. That one will be the "bottom" tube in the cascode. The upper tube in the cascode should be right next door with many wires going between it and the lower tube of the cascode. But better for Ralph to just tell you in terms of "V1, V2, etc."

 

If you have a 5-driver-tube MA-1, posted on December 31, 2014 at 12:06:40
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 It has a CCS, driver tube and three tubes in the voltage amplifier.

One is at the top of the differential cascode and the other two are the bottom of that circuit and in parallel.

Its the bottom tubes that are most important to the sound, followed by the top tube in the differential cascode.

There was a convention established in the M-60 and we have kept with that in the MA-1. So:
V1a and V1b are the bottom of the differential cascode and are the input tubes.
V2 is the top of the differential cascode. V3 is the Constant Current Source, V4 is the driver tube.

For MA-1s with the longer chassis, the order is, starting from the corner of the amp facing the power supply: V3, V1a, V1b, V2 and V4 is in the corner facing the power tubes.

For MA-1 MkIII chassis (17" wide with rounded front corners)

the tubes in the rear are V1a and V1b, the tubes in the middle are V2 and V3; V2 being on the left. V4 is in the front.

Note: V4 should be a -GTA or -GTB if using NOS types.

 

RE: If you have a 5-driver-tube MA-1, posted on January 1, 2015 at 09:09:22
Banat
 Mr.Karsten


First of all Happy New Year for You ,for your great Manufacture and for Everybody else on this cool OTL Asylum forum .
-----------------------------------------------------------------
And I have one friendly suggestion for future Atma-Sphere OTL amps production ,
any tube on amps chassis need to have `old school` stamped sign beside to associated tube socket ,
for example V1 stamp for sonically most sensitive tube of input diff.voltage amp , V2 stamp for upper cascode tube , V3 stamp for associated CCS tube , V4 stamp for driver tube , V5 for..,V6 for.., and so on , depending from particular Amps model, function and numbers of tubes ,
I think that in this way with stamped lettering on amps chassis altogether with associated customer clear operational manual customers can have easy orientation when they want to experiment with different tube brands for Atma-Sphere based audio gear .

 

Hi, Banat…., posted on January 2, 2015 at 08:19:08
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Happy New Year to you, too.
I wonder what you think about using CCSs in circlotron. See my thread below. Have you thought about it or tried it? Thanks.

 

RE: Hi, Lew, posted on January 2, 2015 at 12:38:07
Banat
 Many Thanks and Happy New Year to you, too!
---------------------------
And yes I will give mine thinking about CCS in circlotron but on that thread from below .

 

RE: If you have a 5-driver-tube MA-1, posted on January 4, 2015 at 10:19:03
throwback
Audiophile

Posts: 762
Location: Colorado
Joined: December 8, 2003
 Thanks, Ralph. That helps.

 

RE: 6SN-7's, posted on January 4, 2015 at 20:24:09
throwback
Audiophile

Posts: 762
Location: Colorado
Joined: December 8, 2003
 That does it for 6sn7's. Thanks, guys.


But how about 6AS7's? Each of my Atma M-1 monos has an array of 7 pairs of tubes. Is there an order of preference here as there is with the input tubes? I can imagine that the first pair in the array "sets the tone" for what follows and therefore contributes the most to good sonics. I dunno.

The premium 6as7's seem to be RCA's and Genelexes. No way I could buy 28 of the suckers (maybe Warren Buffet could stake me. "Warren . . .?" Nah, I didn't think so.), even if I could even FIND that many.

But maybe the first pair in each amp? Hmm. Maybe. . . if that would do any real good.

Comments?

 

RE: 6SN-7's, posted on January 5, 2015 at 04:04:23
Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004
 throwback. STOP!!!.
Under no circumstances do you try RCA 6as7's.
The only tube is the Russian equivalent. 6H13 etc.
Read through the archives here at the asylum. PLease.

 

Quick ebay search, posted on January 5, 2015 at 05:14:20
Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004
 Just did a quick ebay search.
I haven't replaced my tubes in a long time, so forgot the actual designations.
6H13C is the same as 6N13S. This is the 6AS7G you should use.
Beware, there is no such thing as a matched pair. As this tube warms up, it's parameters change. If someone says it's a matched pair, it is only being tested with a fixed bias tester. This tube should be checked with a continuous bias machine.
As a fellow lucky owner of the MA-1, we get to bias the tube banks ourselves.

 

RE: 6SN-7's, posted on January 5, 2015 at 07:24:22
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Pursuant to what Cousin Billy wrote, you would be best off buying your 6AS7s from Ralph. Like CB says, the Archives are full of posts about how apparently boutique 6AS7s (like those RCAs and Genelexes) fail to perform or just plain fail in our amplifiers.

 

RE: 6SN-7's, posted on January 5, 2015 at 07:39:39
throwback
Audiophile

Posts: 762
Location: Colorado
Joined: December 8, 2003
 Good advice, guys. Thanks. But I am still curious as to whether I would need to replace the whole string or whether there would be any benefit to replacing just some of them.

Anyway, I'm off to CES today in Vegas. Unfortunately, the THE show has abandoned that particular ship for Newport, so fewer crops to harvest this year.

Cheers

 

RE: 6SN-7's, posted on January 5, 2015 at 07:51:55
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Chuck, You wrote, "I am still curious as to whether I would need to replace the whole string or whether there would be any benefit to replacing just some of them." The answer depends upon what "benefit" you seek. If the existing output tubes are nearing the end of their useful lives, you'd best replace them all in one fell swoop. If you perceive that one tube or more than one is noisy, then you'd need to do some experimentation to identify the culprits and replace them specifically. But to the general notion that replacing one pair of tubes at random in a 14-tube output stage would have some aural benefit, like bypassing an electrolytic capacitor with a good film capacitor, nix on that, IMO.

 

RE: 6SN-7's, posted on January 7, 2015 at 05:20:23
Catastrofe
Audiophile

Posts: 93
Location: St. Louis
Joined: August 10, 2002
 I have MA-1 Silver Editions, and have not found an audible difference when replacing a single bad 6AS7 vs a pair. It's much more important to focus on the 6SN7s in the cascode circuit.

 

6SN-7's, do you own an Amplitrex Tube Tester?, posted on January 20, 2015 at 05:25:36
Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004
 I can't stress strongly enough how important a great tube tester is. The Amplitrex allows us to test in both fixed bias, and continuous bias mode. In continuous you get a true reading of how a tube behaves, especially as it warms up.

You start by testing in pairs. Look to see how the left and right banks age. Upon completion you total the readings from each bank. Don't just total GM. Voltage V is just as important. The first thing you'll notice, over time, the banks equalize themselves. What a great amplifier the MA-1 is.

Since your strongest 6AS7's do more work, they age a little quicker. After time things start to balance. Pay attention to have the same number of newer stronger tubes per bank.

I have never replaced all the tubes at once. Be careful to add up the totals of each banks tubes. It is preferable not to have one side stronger than the other. Placement in the bank appears not to make a difference.

Years ago Jack Williams commented that while GM is important, make sure the V (for voltage) is also well matched. Discard any run away tubes. These are the one's that just keep rising while under testing. I'll guess that I encounter one out of every twenty I test.

 

Tung-Sol roundplates! I'm quite late to this discussion, and you've probably done..., posted on March 21, 2016 at 16:33:34
jeffreybehr
Audiophile

Posts: 5719
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since: December 13, 2004
 ...some tube replacements, BUT...I and MANY others believe that the WWII-era Tung-Sol roundplate 6SN7GT (aka VT-231) is the best-overall-sounding 'N7 that man ever made. To my ears they're SLIGHTLY warmish (but NOT dark, which describes a low level of treble energy) and never harsh in the treble. They're also expensive, but lots of us believe that it'll be money well spent.

Fortunately for me, I still have about a dozen left from my accumulation starting years ago. I believe I'll be using a gain-reduction plug in V2 and either a pair of Ralph's originals or 1960s-era Russian (labeled CCCP!) tubes I got from Upscale Audio some years ago in the V4 position which is a cathode follower.

 

RE: If you have a 5-driver-tube MA-1, posted on September 9, 2023 at 06:44:51
MP
Audiophile

Posts: 44
Joined: July 2, 2001
 Ralph,

What does the V3 CCS tube become, when the longer chassis silver edition is updated to MK3.3 status? Part of the top of the differential cascode, V2 a or V2b?

Received an used MA-1 silver edition MK3.3 yesterday, trying to figure out each driver tube function. (Believe Chuck was the previous owner).

My understanding of 6SN7 driver tubes layout is (facing amp): left most near power tubes is V4 driver, right to V4 is V2, right to V2 are V1a/V1b running, right most near power supply is V3. There is solid state CCS in MK3.3.

The MA-1s drive Quad 989 beautifully, much better than M60. Much more gain (25db vs 20db), and control.

Thank you

 

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