Tube rolling thread for Stereomour II

[oguinn]

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.

[oguinn]

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. 

[oguinn]

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

[Raymond P.]

I've had my newly built SII for about 2 weeks now and was able to compare the stock GE 12AT7 to a pair of Tungsram ECC81's. I've attached a couple of pictures comparing their physical constructions, with the GE on the left. Soundwise, here's a quick description: They are very similar in bass and mids. Bass is impactful and quick, and the mids sound natural and neutral. The highs are the distinguishing characteristics. The GE highs are a bit harsh and peaky, whereas the Tungsram's are smoother, more even, but without loss of detail.

[Paul Joppa]

Sweet - thanks for sharing!

If you got them recently, please post again when they have some burn-in time (especially the GE) - sometimes there is a break-in effect, but not always. Even tubes that are used but have sat unused for years might still need to be run in for a while to be at their best - it would be great to get more data.

[Raymond P.]

Sweet - thanks for sharing!

If you got them recently, please post again when they have some burn-in time (especially the GE) - sometimes there is a break-in effect, but not always. Even tubes that are used but have sat unused for years might still need to be run in for a while to be at their best - it would be great to get more data.

The GE's probably have at least 70 hrs on them. Right now I'm enjoying the Tungsrams, but maybe later I'll put the GE's back in for further burn-in to see if there would be any difference.


I should also note that one of the GE's is weaker than the other, as evident from the driver triode plate voltage being ~235V, which is at the high end of the spec'd range. The "normal" tube's plate voltage is ~215V. Swapping sides shows that the other triode of the weaker tube is also weak. So maybe the condition of this weaker tube along with the mismatch between tubes results in what I'm hearing.

[Tom-s]

GE 12AT7 to a pair of Tungsram ECC81's

As i said on the previous page, the Tungsrams are some seriously obese tubes. 

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

The "Mullard flash" is also normal on most Philips tubes from other factories (also normal on GEC tubes).
It's a result of the current in-rush property of cold filaments/conductors (the resistance rises with temperature).
Don't worry about it. I've even seen tubes where 1 filament did flash and the other didn't. Never had trouble with any.

I've just started tube rolling with the SII and found one very interesting result. There's tubes that are preferred with my speakers (Klipsch Heresy III's), not with the headphones AKG K1000's and vice versa.
For instance: Telefunken ECC81's, love them with headphones (great frequency extension, huge soundstage, etc etc, a bit much of bass), but with the speakers the voices are placed so far back they sound distant/damped/faint. This difference ain't small and is due to both the transducer (speaker vs headphone) as the effect of the room on sound from speakers.


I haven't found the time yet to compare tubes. Mainly because i'm upgrading some caps in the SII first (done with PS, parafeed and coupling caps, cathode bypass to do). In the testbox there's 10 pairs of Eu tubes at this point: Telefunken ECC81/801s, Hamburg 6201/PW, Blackburn TK1, Heerlen TK1, French 6201's (double and tripe mica), Brimar 6060's and General Electric Company 2900's.

EDIT:

My review for now (with speakers).
ECC81 TK1 Heerlen factory (Foil D getter): Full, warm, detailed; has "musicality"; recommended.
ECC81 TK1 Blackburn factory (square getter): Detailed, more analytical sounding tube, sparkle up top (a bit much for me, crazy prices, not recommended).
6201 Hamburg factory (gold pins, round foil getter): Warm, big soundstage, good details yet musical (found for 50€/pair on that selling website, recommended).
6201 PW Hamburg factory (gold pins, dual support halo getter, pinched waist): very close to normal Valvo, unobtanium, not recommended)
ECC81 Telefunken Berlin factory: Air, detailed, missing midrange some sort, analytical.
ECC801s Telefunken Ulm factory: Air, details placed in good soundstage, nice bass (not cheap +-150-200€/pair, but recommended).

[Tom-s]

Rolling output tubes. First up. The RCA single plate. "The original 2A3".

This is a pair i've been waiting to try for very long.

I've changed the operating point on my SII to suit them. I would not recommend using a pair like this in a normal Stereomour.

These are paired with my most used drivers, GEC A2900's.

The warranty band says 20 June 1936.

Only this morning i've tested them for the first time, and both show 80-90% (in the good section) on my EICO 666.

How do these sound? I have no clue how to say this.
Very open, large, palpable in the midrange, easy to listen to.

So, what does this mean?

Detailed on top. Lacking a little bass (compared to Sovtek 2A3 and RCA black plate (single/double DD getter). Bringing out every detail and the music seems more detached from the speakers.

These are like headphones that are so easy to listen to that you just have to turn up the volume.

I like them. If this is the involving type of sound (I obviously don't know how to express myself here) people talk about with EML 2A3 Mesh, those are my next tubes.

Fun fact. Did a picture in the dark. And my camera picks up fluorescense inside the glass bulb of the right example that can't be seen with the naked eye. See picture.

[Tom-s]

A small word of warning for those interested in buying 2A3 monoplates.


These are actually very very fragile tubes. And it's more easy to find duds than it is to find actually good pairs.
The heater wires in these consist of a single string with 10 (or 20, depends how you count) very thin ascending wires that are suspended inside it's plate structure.
These wires are so thin that they easily burn out/break. All later 2A3's went to a more sturdy filament configuration.
Such a break is easy to spot when buying in person, but not when just buying online (like my tube below).
Always look at every filament wire to see if it's still connected properly. And take a pocket resistance meter with you to check for breaks/shorts.
In other occasions the tube looks perfectly fine but has a cathode -> grid leak. This can't be seen or measured easily without actually testing it.

Here's a picture of a Sylvania monoplate that was DOA. I don't know if it can be seen. But the left 5 heater wires are broken. I unfortunately wasn't able to spot this in the online add.

[oztayls]

From what I've read in various forums on the 6201, it's essentially a ruggedised 12AT7 and seems to be superior in just about every way, a considerably more reliable tube given the harsh testing parameters they must endure. I guess the only thing that was never tested for the 6201 was how well it adapted for audio use and how they sounded, subjective parameters anyway. With so many audio circuits, that would be near impossible to test, and a 6201 would perform differently in each case and human ears are not reliable as test machines! Apart from electric measurements, parameters such as Microphonics, resistance to vibration, and duty cycles of the 6201 would be far superior to the 12AT7, and only matched by the military versions of these.

I've had experience of military grade tubes in some other amps, for example the Russian made 6P15P, 6N2P, 6N1P etc, usually with the mil spec extensions -EV/ER after the tube type. Without exception, these were sonically superior to the non-military ones. The question I have is, should we expect the same of the 6201s?

[Doc B.]

You can buy batches of used 12AT7s for not too much money on eBay, and chances are good that a batch might contain a 6201. I'd suggest doing your own research.

[oztayls]

OK, thanks Doc. Do tubes need to be matched?

[Doc B.]

It's not terribly important. I'd just look for two that have the same internal construction.