Help me identify this 12ax7a

[12afael]

I got a famous artist main amp and I'm trying to replicate it before I have to return it. I can't say who for the moment...

I have a donor amp that is same year not so far apart in serial but they sound quite different. The donor is a clean amp while the "artist" have seen a over 30 years of rock n roll( you can smell it!).
I have measured a lot of stuff and all the pots show less resistance but even matching them there is still a big difference. I narrow a big part of the difference to the first tube a 12 ax7a.

it just say 12ax7a, it have a reverse number 5 in the bottom, double mica in the top and a ring of getter residue around it. the Getter is a square solid metal piece and is supported by two wires. the upper mica looks riveted to the main structure. the bottom looks a bit cloudy and milky.

 

[12afael]

according to this Identifying Vintage NOS Vacuum Tubes by Brand Country and EIA Code it should be a mullard but the photos I have seen of mullards are nothing like this one.

 

[gyraf]

..the evacuation part, the top, looks very chinese-around-year-2000. So does the red paint for marking.

You see these in cheap "tube" condenser mics, and they are all-over spec-vise. Perhaps it was selected for it's character on-purpose?

 

[scott2000]

very chinese-around-year-2000

My first thought was National

 

[12afael]

yes I came to the conclusion that is a chinese manufactured tube, fender had it at some point, golden dragon, Valve tubes, shuguang. maybe shuguang is the manufacturer.


I believe it was selected, it have a compression characteristic that make it sound "album ready" and the rest of the preamp tubes are JJ. just the first and more important is this strange one.

The National made in China looks very similar too. but National had Yugoslavian tubes too very different looking.

thanks

 

[gyraf]

IIRC, National was just a branding/distribution service - I have a stash of Japanese national-branded ECC82 somewhere

 

[rackmonkey]

IIRC, National was just a branding/distribution service

Yep, you're right. A tube in a National box is like the proverbial box of chocolates. You never know what you're gonna get. Especially in the late 70s and into the 80s, as high quality Japanese and US manufacturing went away, they were re-labeling some really low quality tubes. Prior to that, they were generally quite good.

 

[Tubetec]

Id say definately Chinese made by the looks , usually very poor and microphonic right out of the box , could easily cause the loss of clean tone like you describe . Try subsititute a known bad tube for comparrison

 

[emrr]

There were a ton of Westinghouse 6L6's that came on the market around 2000, they were all new production in NOS boxes! I was somewhere around that time and saw a ton of those same surplus Westinghouse boxes that were unused, still factory flat.

 

[mhelin]

Same tube in youtube:

 

[mhelin]

And here ... broken:
https://www.gad.net/Blog/2011/07/08/death-of-a-vacuum-tube/

 

[mhelin]

It gets interesting:
https://www.gad.net/Blog/2011/06/07/how-to-capture-brian-setzers-tone/

A NOS chinese tube?

Propably Shuguang made in now closed Beijing factory.
Like this one:
https://nesstone.com/product/unused-oem-shuguang-12ax7-ecc83-preamp-tube/

 

[12afael]

This new old stock 12AX7-A ECC83 Foil Getter preamp tube was made by Shuguang in the now closed Beijing factory. Mesa branding. They are the highly sought after version that are no longer made and getting difficult to find. It is a high quality preamp tube and is regarded for its clarity and brightness. They are stock tubes in many amps including Marshall and Mesa Boogie. Considered by many to be the best sounding preamp tube available.
Here is what one of my customers wrote about them:
“NOS Shuguang Foil 12AX7 preamp tubes! Excellent Quality! Woke Up My JCM 800! A+!”

Thanks Mhelin ! very inetresting the Setzer connection.
I traced the curve of the tube and other tubes (i still have a lot more to trace) it behave definitely different than the other tubes

 

[12afael]

The left one is the Chinese tube, the right one is a new JJ. I have other Chinese tube from an 80s valvestate amp but it does not behave the same.

 

[Walter66]

Sorry, don't know how precious your time is with such a small repair or overhaul job of an amp.
With every amp of quality, delivering to a good musician, I would never put this kind of crap tubes into service.
Because, you don't know it's heritage, you don't have experience with the tube manufacturer (nothing is prooved here, just speculation), but you should guarantee that this amp will sound excellent and has long life ahead.
So why not use a good NOS example and you'r done. Usually, half an hour of work done by a professional is worth 40€=$40. For that amount, you should find a fine 12AX7 NOS, don't have any other struggle and be done. But I bet, you have invested more of your time finding out specs for this rubbish electron tube.
I would put this out immediately, you will see, others will sound much better.

P. S. Sorry, I've never seen this type of ECC83 and that is, because I only use NOS good parts and not chinese cheap tubes. They mostly sound awful compared to the best.

 

[dai h.]

bit on info in an old issue of Vacuum Tube Valley (page 5) :

https://worldradiohistory.com/Archi...m-Tube-Valley/Vacuum-Tube-Valley-Issue-14.pdf
(also a bit more info on 12AX7/ECC83 in general in an earlier issue) :

https://worldradiohistory.com/Archi...m-Tube-Valley/Vacuum-Tube-Valley-Issue-01.pdf
(I thought they were Shuguang but apparently from the "Sino" factory, at least according to the (issue 14) article.) From what I vaguely remember, something happened to the factory and the later ones (which appear the same) don't have a good reputation. I've used the earlier ones in a couple of guitar amps, and they were okay. Low microphonics (maybe the shiny stiffeners help?). They seemed to be widely used and sold (IIRC I bought some from Mesa/Boogie in the '90s--I think they even had a special (supposedly) low noise version with a piece of shrink wrap around the tube called "SPAX7"--bit dubious about that in hindsight).

 

[12afael]

Walter66 I understand your point. I get paid for it and I found it interesting. "Sound better" is a very subjective topic.

When I tried the donor amp it sounded better to me, more dynamics, more low and hi end. But when I tried the original amp it sounded exactly like the album right away. I would have to eq the donor and compress it and it would never be the same. This guy have 5 of this amps and this is the number one, the one he have used for every album since begining of the 90s.

It remember me a story that our Bo Hansen Hansen told me when I visited him in Gothenburg (this is how I remember it, maybe Bo can correct me)

A guy came to Bo store and he talked with him for a while. He seemed old customer. When he left Bo told me he was the guitar player of Santana's band. Once he took his amp for repair and Bo noticed that the bias was wrong so he fixed it. Time later the customer returned angry you broke my amp it does not sound the same. Bo had to put the bias back as it was to make it sound "right" again.

Similar to this amp or Brian Seltzers guitar amps are extensions of the instrument we want them to sound right for the player.

Thanks Dai that is very interesting

 

[Sistersandoz]

I bought a 1984 Mesa Mark IIC+ Mint. These square foil getter chinese tubes were in all 4 positions. 2 with shrink wrap. Acid wash markings say Mesa STR 12AX7A ECC83. I have also discovered this same tube out of a 92 block letter 5150 and had Peavey Super 7 on it. I have about a dozen of these now and have been magic in every amp I have tried them in. 4 of them are in a Triple Rectifier with V5 being a Philips Miniwatt balanced triode made in Holland. I have found out from Mesa they used these tubes up until 1996 when the Beijing Factory closed. Hard to find but Im always looking for them. The current china made tube that looks similar in plate construction has a round halo getter and is thin and not close in comparison. I have seen them branded as Fender, GT, Marshall and ARS. Great tube. I have not found a bad one. Supposedly they were 6N4 7025 military grade. I found this post and forum searching for this tube. Im not a tech, just a guitarist that listens closely. Lol.

 

[Sistersandoz]

 

[Newcruzer21]

You might check out this tube on Ebay...
Looks similar with rivets on top mica and getter banding between the top 2 mica plates>

https://www.ebay.com/itm/3347037066...55-0&campid=5338722076&customid=&toolid=10050