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-   -   How to select a good Hifi 12AX7 tube? (http://www.diyaudio.com/forums/tubes-valves/239022-how-select-good-hifi-12ax7-tube.html)

aliwang 11th July 2013 08:21 AM

How to select a good Hifi 12AX7 tube?
 
Hi, guys!
I heard a good hifi 12ax7, must pass the following test
IP Emission
GM
H-K Leakage
Gas
Noise
have any other item?
The parameters for each item what conditions must be met?

Thanks!

ingenieus 11th July 2013 01:03 PM

Here is some info on the differences between 12AX7 tubes from different manufactures.

http://www.amplifiedparts.com/tech_c...ent_made_tubes

http://www.worldtubecompany.com/mm5/...vc?Screen=TF-2

My own selection criteria would include a good price from a trustworthy supplier.

artosalo 11th July 2013 05:07 PM

Quote:

Originally Posted by aliwang (Post 3557375)
Hi, guys!
I heard a good hifi 12ax7, must pass the following test
IP Emission
GM
H-K Leakage
Gas
Noise
have any other item?
The parameters for each item what conditions must be met?

Thanks!

Most of those are such features that the manufacturers do not even specify/present to users.

For me it is diffucult to think what I could benefit for such information.
Typical published specifications are more than sufficient.

ruffrecords 11th July 2013 05:27 PM

The construction of the 12AX7 variant probably has more effect on performance than anything else. My own test have shown that long plate types have measurably lower distortion than other types. If you plan to use ac heaters then a spiral wound filament can be an advantage. My preferred version is the 12AX7LPS.

Cheers

Ian

kevinkr 11th July 2013 06:49 PM

I'll second the 12AX7LPS, I have found it to be a good performer and reliable.

artosalo 11th July 2013 07:20 PM

According to my measurements the Soviet 6N2P(-EV) has lowest input capacitance.
Essentially lower than long plate versions.
I can also confirm the lower THD of LPS version.

Gost22 12th July 2013 09:57 AM

2 Attachment(s)
Hi guys!
Please comment on this tube ecc83, since many use it.:rolleyes:
thank you!

kevinkr 12th July 2013 07:48 PM

SY likes the JJ as an economical and good performer. (I do too, but think they are somewhat short lived from direct personal experience) I think at a certain point this discussion becomes academic, there is nothing like direct experience as opposed to hearsay and opinion. Just go out and buy some, look for bargains at radio shows, antique shows, flea markets, ham fests and online.

Grab:

7025
6681
5751 (near equivalent)
E83CC
ECC83
12AX7
12AX7A
12AX7WA

Shop carefully and at least some can be had for little money. Buy reasonably priced modern production as well as anything vintage that catches your eye.

My best recent score was a quartet of early 1960s vintage Telefunken EL84 and three Telefunken smooth plate ECC83 pulled from an abandoned stereo console down the street from my house. All tested as new.. FREE!

hpeter 12th July 2013 09:12 PM

what i hate about JJ is they put everywhere "S", even when tube has no extra specs like NOS had.

v4lve lover 13th July 2013 05:39 PM

S means frame grid as per the Telefunken designation.


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