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Mysterious 12AU7/ECC82 Vacuum Tubes

post #1 of 18
Thread Starter 

I have recently taken the risk to purchase NOS vacuum tubes from a well-known auction site. While they appear original and the sellers have extremely good reputation, I cannot find background information on the origin and quality of these tubes.

 

In my previous research, the only information that I could find was that a very limited number of other people had the same tubes. I'm guessing they're either copies, rebrands from other manufacturers, or rare. I am looking for vacuum tubes experts who could perhaps help me shed light on these unsolved cases and determine which of these 3 hypotheses is the right one.

 

Eventually I will give the tubes a listen, which could provide a valuable clue, but right now I am waiting for a fuse to convert the concerned amplifier's voltage to 110V.

 

Case #1 - Amperex Orange Globes from West Germany

 

I have owned many Amperex Orange Globes of various types in the past, and it was always of my understanding that they came from a factory in Heerlen, Holland. However, this box of 5 tubes is apparently from West Germany, according to the printing. There is also a code in yellow that I haven't seen before on Holland-made Amperexes. I can't recall if they have creases on the top - I will check when I come back home for the weekend. There are no creases on the top.

 

http://gyazo.com/a356ebc16f3f54b6e23b33f9886c9c44

http://gyazo.com/7a9296144f49ac707df6d8d4fc8cd117

http://gyazo.com/27551dd34ecef61f1f2fb83bf55bdd96

 

 

Case #2 - Shield-less Mullards

 

Apart from some military models, all the non-rebranded Mullard 12AU7's that I have seen in the past had a shield logo or a similar shield-like symbol. These, however, simply have the name "Mullard" printed in big characters. They have two faint creases on the top.

 

http://gyazo.com/3dee5ae6db22d93efa0f910a780effe4

http://gyazo.com/882e8e085156a1e8c4387abd6e55e15d

http://gyazo.com/ca3234cddaeba9362d41263415ea9c02

http://gyazo.com/1280c4358a084aad48729292778ab16c

 

Let me know if you'd like any other information, and thank you very much for your help.


Edited by Benjamin6264 - 3/24/13 at 11:58am
post #2 of 18

You can check if the Amperex have a diamond shape on the bottom?  Maybe a Telefunken rebrand?  I doubt it though.  If not Siemen is my best bet. 

post #3 of 18
Thread Starter 
Quote:
Originally Posted by Neogeo333 View Post

You can check if the Amperex have a diamond shape on the bottom?  Maybe a Telefunken rebrand?  I doubt it though.  If not Siemen is my best bet. 

 

Will check that this afternoon. Thanks for the input.

post #4 of 18
Thread Starter 

I'm back home, and the Amperexes don't have the TFK diamond symbol. Siemens rebrand seems like the most probable hypothesis as of now. Also, there are no creases on the top.


Edited by Benjamin6264 - 3/24/13 at 10:18am
post #5 of 18
Thread Starter 

New question: I have purchased some Mullard EL34's, and one of them seems to have a small chip coming from the circular disc between the plates and the getter. Is there any risk of it causing a short-circuit if it falls in the bottom and touches two wires, or is the substance forming the said disk non-conductive? Thanks in advance.

post #6 of 18

When you get them, take some higher res, macro shots... showing the insides better.  Let the tube experts try and ID them based on whats on the inside.  If theres no diamond logo embossed/stamped into the glass base its not a telefunken.  epay sellers are usually pretty quick to pick this up and they will price hike a legit Telefunken re-brand accordingly.  Its rare that a diamond embossed tube goes out un-noticed.

post #7 of 18
Thread Starter 
Quote:
Originally Posted by kramer5150 View Post

When you get them, take some higher res, macro shots... showing the insides better.  Let the tube experts try and ID them based on whats on the inside.  If theres no diamond logo embossed/stamped into the glass base its not a telefunken.  epay sellers are usually pretty quick to pick this up and they will price hike a legit Telefunken re-brand accordingly.  Its rare that a diamond embossed tube goes out un-noticed.

 

Only my actual TFK tubes have the diamond logo, so no Telefunken rebrands in this lot.  I will take some macro shots like you suggested; thank you!

post #8 of 18
Quote:
Originally Posted by Benjamin6264 View Post

Let me know if you'd like any other information, and thank you very much for your help.

 

Any etched codes on the tubes?

 

Quote:
Originally Posted by Benjamin6264 View Post

I'm back home, and the Amperexes don't have the TFK diamond symbol. Siemens rebrand seems like the most probable hypothesis as of now. Also, there are no creases on the top.

 

That doesn't sound like Siemens to me.

 

Quote:
Originally Posted by Benjamin6264 View Post

New question: I have purchased some Mullard EL34's, and one of them seems to have a small chip coming from the circular disc between the plates and the getter. Is there any risk of it causing a short-circuit if it falls in the bottom and touches two wires, or is the substance forming the said disk non-conductive?

 

“The mica group represents 37 phyllosilicate minerals that have a layered or platy texture. The commercially important micas are muscovite and phlogopite, which are used in a variety of applications. Mica’s value is based on several of its unique physical properties. The crystalline structure of mica forms layers that can be split or delaminated into thin sheets usually causing foliation in rocks. These sheets are chemically inert, dielectric, elastic, flexible, hydrophilic, insulating, lightweight, platy, reflective, refractive, resilient, and range in opacity from transparent to opaque. Mica is stable when exposed to electricity, light, moisture, and extreme temperatures. It has superior electrical properties as an insulator and as a dielectric, and can support an electrostatic field while dissipating minimal energy in the form of heat; it can be split very thin (0.025 to 0.125 millimeters or thinner) while maintaining its electrical properties, has a high dielectric breakdown, is thermally stable to 500 °C, and is resistant to corona discharge. Muscovite, the principal mica used by the electrical industry, is used in capacitors that are ideal for high frequency and radio frequency. Phlogopite mica remains stable at higher temperatures (to 900 °C) and is used in applications in which a combination of high-heat stability and electrical properties is required. Muscovite and phlogopite are used in sheet and ground forms.” (http://en.wikipedia.org/wiki/Mica)

post #9 of 18
Thread Starter 
Quote:
Originally Posted by Oskari View Post

 

Any etched codes on the tubes?

 

 

All the Amperexes have "9-50" printed in orange.

 

Three of the Mullards have the code "Gf1 B4D2" etched, and the fourth Gf1 B4D1, but the code is upside down on that one.

 

Also, thanks for the info on mica - my only worry now is that the chip will maybe induce a bit of noise, but I will see soon enough if that's the case.

post #10 of 18
Quote:
Originally Posted by Benjamin6264 View Post

All the Amperexes have "9-50" printed in orange.

 

That's a Y-WW date code printed with the Amperex label. The yellow print is more interesting.

 

Is there a metal tab inside the tube with characters on it?

 

Better photos might help.

 

Three of the Mullards have the code "Gf1 B4D2" etched, and the fourth Gf1 B4D1, but the code is upside down on that one.

 

Those would be Mullards made at Blackburn (B) then.

 

Also, thanks for the info on mica - my only worry now is that the chip will maybe induce a bit of noise, but I will see soon enough if that's the case.

 

I think that's unlikely.

post #11 of 18
Thread Starter 
Quote:
Originally Posted by Oskari View Post

 

That's a Y-WW date code printed with the Amperex label. The yellow print is more interesting.

 

Is there a metal tab inside the tube with characters on it?

 

Better photos might help.

 

 

That would mean they were made in the 50th week of year...9? Could it be the the 9th week of 1950 rather? Or perhaps some writing is missing, although it doesn't seem so.

 

The yellow printing indicates "ECC88" horizontally, and "DC" vertically right under.

 

I forgot to take some pictures while I was at home; I'm back at the university dorms for the week. I'll make sure to take the macro shots this Friday.

 

As always, thanks a bunch for the help. I will check for the said metal tab.


Edited by Benjamin6264 - 3/25/13 at 1:33pm
post #12 of 18
Thread Starter 
Quote:
Originally Posted by Oskari View Post

 

Those would be Mullards made at Blackburn (B) then.

 

 

Awesome! That solves one of the cases. I'm still curious as to why they don't have the usual logo though.

post #13 of 18
Thread Starter 

New case! :)

 

I have just managed to grab a trio of tubes that I think are the elusive Siemens silver/nickel/chrome/shiny plates. Could anyone please confirm from the pictures?

 

http://gyazo.com/fef3c05931747eaa1bc6b6049a074c00

http://gyazo.com/997d057edf008013d541566b14f064cc

http://gyazo.com/fbf873dac0e31b8c86d0dfa5c6ed81ac

 

 I have compared the inside structures and cannot find a difference. Is there any other manufacturer that has made similar tubes?

 

From the auction listing: "One Eico branded tube has a code #2B and the two Pacotronics branded ones have no ledgible code. The structure of all three look the same to me and have dual getter posts". The seller has 100% feedback with 1364 transactions.


Edited by Benjamin6264 - 3/27/13 at 12:11pm
post #14 of 18

Benjamin6264,

 

May I suggest sending Steve at Mullard Magic (www.mullardmagic.co.uk) an email explaining your quandry. Steve has an encyclopaedic knowledge of all things thermionic and is an extremely affable guy too, so I'm sure that he'll be able to help you.

 

Cheers,

 

Andy.

post #15 of 18
Thread Starter 
Quote:
Originally Posted by smial1966 View Post

Benjamin6264,

 

May I suggest sending Steve at Mullard Magic (www.mullardmagic.co.uk) an email explaining your quandry. Steve has an encyclopaedic knowledge of all things thermionic and is an extremely affable guy too, so I'm sure that he'll be able to help you.

 

Cheers,

 

Andy.

 

I sent him an email. Thanks for the suggestion!

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