12AX7 structure comparison

Luckie · #1 08-20-2011, 06:34 PM

I was replacing the preamp tube in a valve junior, and I figured I'd take a photo of the tube I replaced, and that I replaced it with.

The Chinese one looks scared.

hexbass · #2 08-20-2011, 06:36 PM

Yup-- check out the diff between a 12 ax7 and a jan 5751, also check out the tone!!

throbgod13 · #3 08-20-2011, 06:37 PM

they are all have different internal structures.. i'd google info about what makes them different.. i.e. long plates, short plates, halo getters, etc..

you'll be amazed at what you'll find..

the RCA RC-30 tube manual is something that you'll want to find if you get into tube amps..

JimmyM · #4 08-20-2011, 06:37 PM

Ya, for pre tubes, I only buy NOS nowadays unless it's a dire emergency. Your pic is a lot of the reason why. You can find good new tubes, but they're still a little too hit and miss for my tastes.

throbgod13 · #5 08-20-2011, 06:39 PM

NOS is the only way to go..

Volume4 · #6 08-20-2011, 10:03 PM

Excellent 12AX7 choice...all the Philips ECG tubes are great, pre or power.

Comparing this particular Chinese 12AX7 to a Jan Philips ECG is really extreme. Thats a very rugged military spec tube next to an no brand bulk OEM tube out of a $130 tube amp.

There are some good new 12AX7's being made (thats not one of them), but those JAN Philips are some of the toughest tubes ever made.

Bongolation · #7 08-20-2011, 10:40 PM

Quote:

Originally Posted by throbgod13

NOS is the only way to go..

For a V1 in a real tube amp, yes.

grendle · #8 08-20-2011, 10:52 PM

Quote:

Originally Posted by hexbass

Yup-- check out the diff between a 12 ax7 and a jan 5751, also check out the tone!!

+++++1000

grendle · #9 08-20-2011, 10:59 PM

Lol, They should assign 12ax7's with a crap tone rating from 5-10.

Luckie · #10 08-21-2011, 02:07 AM

Oh yeah, it's all about NOS...
Gotta find a decent EL84 next.

I know this isn't the "fairest" comparison, and that there are different design techniques employed, but what it comes to is the JAN destroys the Chinese one for tone. It even narrowly edged out a NOS Mullard!

staindbass · #11 08-21-2011, 07:24 AM

el84 ? go with rca blackplates, that my suggestion. they sound better than telefunkens in my orange tiny terror.

staindbass · #12 08-21-2011, 07:25 AM

hey, i never heard of a 12ax7b, whats the difference. **** found it http://www.tubesandmore.com/scripts/...age=12AX7CHART

beans-on-toast · #13 08-21-2011, 08:09 AM

There isn't a single design for the 12AX7 that they are all copying. The designs vary. Some of the reissues are copies, with variations, of the classic designs. They don't copy the exact designs because the cost would be prohibitive, environmental issues, or even loss of the propriety knowledge that went into manufacturing these tubes.

With NOS tubes there were many variations as well. There were consumer, industrial, military, and even space versions. Versions that were meant to be in continuous use, ones that could be power cycled more often, those that had low filament current or different heater voltage requirements for battery operation such as cars and portable military radios, versions that had wider temperature specs, versions that could withstand higher mechanical stress, gravitational force, altitude, etc. Of course there were also low noise versions. There were also variations that didn't fit in the standard 9 pin tube socket. These tubes had different names. They were listed as equivalents.

Every manufacturer has their own take as to what can be labeled as a 12AX7. Today, if it is plug compatible and is close in some of the specs, they'll market it as a variation of a 12AX7.

coreyfyfe · #14 08-21-2011, 08:45 AM

While we're on the subject, is it just me or are many of these modern tubes wider than NOS tubes? I was trying out a variety of 12AX7s I have in my SVT and most of the newer tubes were too fat for the little metal sleeve on the preamp. The NOS tubes fit in just fine.

Groover · #15 08-21-2011, 09:58 AM

I also found the newer tubes a little fatter as well, Tung-Sol are a good example.

To the OP - Have fun experimenting! There are lots of variables when it comes to the 12AX7 (7025, 5751, Long Plate, Short Plate, Black Plate, Gray, Triple-Mica, etc)

I swear by NOS (just like many here) and especially the military version, such as the GE 5-Star 5751.

However, some of the new tubes are very nice as well. Again Tung-Sol 12AX7 is a nice full range tube and readily available.

beans-on-toast · #16 08-21-2011, 10:39 AM

Quote:

Originally Posted by coreyfyfe

While we're on the subject, is it just me or are many of these modern tubes wider than NOS tubes? I was trying out a variety of 12AX7s I have in my SVT and most of the newer tubes were too fat for the little metal sleeve on the preamp. The NOS tubes fit in just fine.

Yes that's a good point. This is a problem with the SVT tube shield collars. The intent is to have them fit close to the tube to help with heat dissipation. I've never found a NOS tube that didn't fit but even with those there isn't a lot of free space around the tube.

For some reason they never used a shield on the smaller 6C4 tube. This tube tends to have problems with microphonics so some damping is a good idea. I solved that by using a Cinch 5020B tube shield. It is a metal case with a band of fingers that contact the tube. It just pushes over the tube and holds itself in place. No special socket is necessary. Not only does it help dissipate heat but it suppresses vibrations. They cost $5.50 at Fair Radio Sales.

seamonkey · #17 08-21-2011, 01:40 PM

Can you imagine how easy it is to counterfeit tubes. Buy a box, unlabelled with the same basic interior, and silk screen on any label you want. Sell for 10-20x the price you payed.
Do you think a company like Philips would do such a sloppy job labeling JAN tubes?
What regulatory agency is watching this industry?

Mr. Foxen · #18 08-21-2011, 01:48 PM

I think tons of old brands were made in not so many factories an labelled to order. Plenty of valves have the same guts as Mullards and a different name on them. What people need to do is judge valves by their function not their age and label.

Luckie · #19 08-21-2011, 05:41 PM

Quote:

Originally Posted by seamonkey

Can you imagine how easy it is to counterfeit tubes. Buy a box, unlabelled with the same basic interior, and silk screen on any label you want. Sell for 10-20x the price you payed.
Do you think a company like Philips would do such a sloppy job labeling JAN tubes?
What regulatory agency is watching this industry?

Aint nobody watching really.
I wouldn't call the labeling "sloppy", it's just old IMO.
I know this is a legit JAN, the guy I got it from is tops.

BurningSkies · #20 08-21-2011, 06:35 PM

Quote:

Originally Posted by seamonkey

Can you imagine how easy it is to counterfeit tubes. Buy a box, unlabelled with the same basic interior, and silk screen on any label you want. Sell for 10-20x the price you payed.
Do you think a company like Philips would do such a sloppy job labeling JAN tubes?
What regulatory agency is watching this industry?

FUD FUD FUD.