Tube rolling thread for Stereomour II

[Tom-s]

Let's start a topic to share experiences with tube rolling in the Stereomour II.

Please share your opinion on different tubes in SII!

SI users are welcome to share aswel!

I'll try to keep this startpost up to date with what tubes to use in SII.

The list of tubes to use in the drivers seat:
12AT7(W)(A)(B)(C)
ECC81
E81CC
ECC801S
6201
6060
CV455
CV4024
A2900
TS65
B309
M8162
7728
6679

Not direct equivalent, optional:
5965 familiy (E180CC = 7062 = CV8431 = 6829 = 6414)
6211


Do note: some have minor electrical differences from ECC81 / 12AT7, but can be used in SII.

The list of tubes to use in the output position:
2A3
5930
VT-95
CV1831
#2A3-40
300B 2.5V (EML (solid and Mesh / Sophia)

! 45 (145,245, 345 etc.)

#The extra power available with these tubes not being used in SII.
! Needs some modification. https://bottlehead.com/smf/index.php?topic=11138.0

The 6.3v heater winding is rated 1.5 amps.

The 2A3 filament windings are actually 3.15 volts at 5.5Arms. (The high current rating allows for DC heating, which is an optional upgrade for those with extremely sensitive speakers.) In both AC and DC cases, the filaments have small series resistors to fine-tune the voltage.

EML 2A3 or 45 tubes in SII: https://bottlehead.com/smf/index.php?topic=3054.0
Guarantee conditions: http://www.emissionlabs.com/cd.htm
So. It's ok in a stock SII. If you replace the interstage coupling (0.1uf, 600V) with a paper in oil type coupling capacitor, it will void warranty.

 

[Jameson]

Hell yes, excellent timing as I’m constructing mine now.

Might I suggest formatting this post the same way as the Crack thread, where there’s a section for tubes that can be dropped in with no mods and a section for tubes where mods are necessary (like it seems to be for ECC81/12AT7 - unless I’m misreading)? You could add 45s to the list of “usable with mods,” right?

EDIT: Ha - looks like you edited this right as I posted to add 45s.

 

[Jamier]

Tom,

    I am not a huge tube roller, but I think the following list are also 12AT7 compatible:

6211
5965
6414
6829
6679
7728
TS65
M8162

I am no expert on these, so part (or all) of this list may be redundant with respect to your list.

Jamie

 

[Doc B]

A lot of those are not directly compatible. They might be a near miss, but they would need optimization of the operating point to perform at their best.

 

[raymondp1138]

Thanks, Tom! I have a SII on order, so I can see this thread to be super useful.
I like idea of categorizing those that are direct drop-ins vs. those that might need modifications.

 

[Tom-s]

Tom,

    I am not a huge tube roller, but I think the following list are also 12AT7 compatible:

6211
5965
6414
6829
6679
7728
TS65
M8162

I am no expert on these, so part (or all) of this list may be redundant with respect to your list.

Jamie

The reason Doc mentioned is the reason i didn't include them in the list.

The 6211, 5965 families are different and need modification.

7728, TS65 and M8162 are special quality equivalents and i'll add them.

A lot of those are not directly compatible. They might be a near miss, but they would need optimization of the operating point to perform at their best.

 

[Tom-s]

So let's discus the different types.

Because i have to do something while waiting for the SII.

First things first.

The ECC81

Mentioned: Dec1950, Market: 1951.
Twin triode, the European version of the 12AT7, especially designed for VHF, also good to use in audio amplifiers; high amplification, low internal resistance.

https://www.radiomuseum.org/tubes/tube_ecc81.html

It is a direct replacement in SII.
From personal experience, don't look at the label of the tubes, look at the tube factory codes for European tubes.
These tell you more about the actual tube than the label does. 

Tube data: https://frank.pocnet.net/sheets/010/e/ECC81.pdf

Philips tube code: https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf

In the Philips ECC81 collection i've seen:
Delta -> Heerlen (The Netherlands)
R -> Mitcham (England) (Mullard)
B -> Blackburn (England) (Mullard)
D -> Hamburg (Germany) (Valvo)
‡ -> Munich (Germany) (Siemens)
F -> Suresnes (France) (La Radiotechnique)

I've added an example. It's an Adzam (Belgium) labeled, Mullard Blackburn factory build, ECC81 pair (three holed plates are typical for certain versions of ECC81 build in this factory).

 

[Tom-s]

The 6201 (12AT7WA). Ruggerized ECC81/12AT7 with military / industrial designation (computer).

Milspec version of the type 12AT7.  Genuine versions of these have extra thick mica wafers to help eliminate microphonics. Some have extra support rods which give even more stability. 

As can be seen in the datasheet, they were build shock and vibration resistant for mobile use. This makes them very usable in audio applications.

Philips 6201: https://frank.pocnet.net/sheets/009/6/6201.pdf

Sometimes these were relabeled ECC801S in Europe. An ECC801S tube is build within the 12AT7WA/6201 spec. But not every 6201 is a ECC801S tube.

Here's a ECC801s (Valvo) from my collection that's build like a Valvo 6201, and a telefunken pair for comparison.
https://ep1.pinkbike.org/p5pb17201911/p5pb17201911.jpg

Telefunken ECC801s datasheet: https://frank.pocnet.net/sheets/117/e/ECC801S.pdf Do note the long life heater specs the 6201 are missing.

 

[Jameson]

Heads up that TubeDepot has a 24 hour sale on JJ 2A3s. 15% off!

 

[Tom-s]

The waiting game for a new Bottlehead kit is always the hardest part...

So! Another tube to roll in SII.

Aside from Philips and Telefunken there's a few other interesting EU tube manufacturers.

The American International Telephone and Telegraph company ITT (Western Electric) had two known subsidiary companies; Brimar (British Manufactured American Radio) and Lorenz (Germany).

The 6060 is an 12AT7 special version from Brimar with square black plates. The ones with the "yellow-T" on the back would be the "special quality" versions according to the internet. The CV4024 (CV=Common Valve, a military designation) is a military designation of this tube. Beware CV4024 is also used for Mullard military Ecc81's.
Other names for a Brimar ECC81 (see below) are CV4033 and 13D9 (these are less known names and can be found for less money because of this).


From the Lorenz company i've found many relabeled versions. Some are called Lorenz, ITT, SEL, others have just written the tube type on them. Common with a lot of these is extra mica supports. And they are physically obese/large compared to ECC tubes from other companies (though not as fat as Tungsram, but close).

From my experience with ECC82's, tubes from these companies are, while found for less money, just as good sounding as other manufacturers'.

 

[Jameson]

I’ve got a set of Mullards on the way. It sounded in your email like you think the smaller tubes have a bigger influence on sound than the 2A3s. I’m curious about that (not doubting you at all, just wondering) since it seems like the final stage would be the most important. Any thoughts?

 

[Doc B]

The least liner tube will tend to exhibit the most influence on the sound. 2A3s, 300B, 45s, 845s, etc. are pretty linear. The small signal tubes are not typically as linear. There are however a lot of other factors that need to be considered in a given circuit besides linearity - gain, maximum voltage output, etc.

 

[Tom-s]

I'm not educated on the electric part.
So i look at it from my simple perspective:

1. Driver tubes make a better option for tube rolling as they are generally >10x cheaper.
2. The second tube in the circuit only amplifies the signal coming from the first tube. This makes the second tube also amplify all the "defects" made by the first tube.
3. Availability and price? Did anyone mention price?  :-X

 

[Jameson]

I’m really happy to hear that since those 2A3s are cost prohibitive to roll whereas I can do a lot more on the smaller ones. Thanks, guys.

 

[Tom-s]

The least liner tube will tend to exhibit the most influence on the sound. 2A3s, 300B, 45s, 845s, etc. are pretty linear. The small signal tubes are not typically as linear. There are however a lot of other factors that need to be considered in a given circuit besides linearity - gain, maximum voltage output, etc.

Linearity, that's the point where certain tubes in the first post seem to differ.

Greater linearity is the reason, some say the GEC A2900's would sound better than your average ECC81. Making them the (being unobtanium) king of ECC81, blabla.

Picture of these.

Edit: I have looked at the tube curves and they do look more linear? But i'm like a blind man looking at these things.

Another quote on linear tubes:

One of the most noticeable changes is that we have gone to a 5670/2C51/WE396A tube as the driver. Why? Partly because a lot of folks found that the 12AT7 had to much gain in their system which led to hair trigger volume controls and a bit more transmission of the noise floor from front end equipment than they liked. The 5670 has a mu of 33 as opposed to the mu of 60 of the 12AT7. The 5670 is also a very sweet sounding, particularly linear tube, that we feel is step up sonically from the typical 12AT7. There’s enough variety of brands to make tube rolling interesting and it is not prohibitively expensive.

Edit: how to use 5670 https://bottlehead.com/smf/index.php?topic=8687.0

 

[Jameson]

Alright, finally! After about 10 days of no forward momentum on my first shipment from TubeDepot they sent along a second package of Electro-Harmonix Gold 2A3s and Mullard NOS 12AT7s (CV4024).

I'm rolling both in this week and I'll share some impressions. I started with the Mullards and noticed a flash at the bottom of each tube on startup that I never noticed with my previous tubes. Anything to be worried about there?

 

[Paul Birkeland]

That is the Mullard flash, and it's normal for Mullard tubes.

 

[Jameson]

Thanks, I wasn't aware that was a thing. Just like I wasn't aware that Sovtek and Electro-Harmonix are the same company so I basically paid a little more for a different brand name.

 

[Paul Birkeland]

I don't believe the Sovtek 2A3 has the gold plated grid wire. 

 

[Jameson]

Ah ok, so there's at least one difference. Money well spent! The Mullard are sounding great so far, though.