Please tell me the difference between 12AX7's & 7025's tubes?

Custom Deluxe

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Can someone tell me the difference between 12AX7 & 7025 tubes? It seems like you see both of these numbers written on the box flap of NOS tubes.

Are they same? It seems like many people say they aren't. Looking to retube a Deluxe Reverb and want to pick up the right stuff.

Thanks.
 

ThermionicScott

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Once upon a time they were different, the 7025 being a special low-noise and -hum version of the 12AX7. Same exact electrical characteristics otherwise, so you can swap one for the other without worry. Modern 12AX7s are generally designed for low microphony, noise and hum, so they slap the "12AX7" and "7025" labels on there without too much afterthought -- it's not like you're going to be buying a 12AX7 for a non-audio use these days, anyway. ;)

- Scott
 

Custom Deluxe

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Scott:

Thanks. I guess that was really my question. When a tube is labeled 12AX7A/7025, is the 7025 listed there as a replacement or equivelent part number?

If a tube is a true 7025, would that or should that be the only # listed on it?
 
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telex76

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The last time I looked for NOS RCA 7025's, they were $125.00 and nobody had any. I have an original 1965 DR that still had original RCA 7025 tubes when I got it. 7025 was the only number on the tube.
 

Joe-Bob

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If a tube is a true 7025, would that or should that be the only # listed on it?

I think it should. As mentioned before the 7025 came about as a low-noise
12AX7, so the specs were for higher quality components. So, while every 7025 is a 12AX7, not every 12AX7 is a 7025.
 

bpinnb

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Lots of old wives tales and misinformation here, so let's try and set the record straight.

In the old days:
12AX7 was the US designation for it's consumer grade version of this tube.

ECC83 was the European designation for the 12AX7 -- the tubes were functionally identical.

7025 was the designation used for a heavy duty version of the 12AX7. Some people refer to this as "military grade" which is a misnomer -- because for the most part, the US military specified heavy duty tubes.

Today, manufacturers are essentially using these three designations interchangeably. Consequently, you'll find various combinations of these designations printed on the packaging and the tube itself.

Unless you can find brand new 7025's made 50 years ago, the 12AX7, ECC83 and 7025 are basically all the same tube. This is not to say that all modern 12AX7's are the same they are not. For example, a Czechoslovakian made JJ 12AX7 will be different from a Soviet-made SOVTEK 12AX7. They will however, be functionally identical and serve the same purpose.

Good Luck!
 
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uriah1

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I always like square getter and triple mica if I am laying out big bucks nowadays.
Military grade JAN 12AX7WA
 

Buckaroo

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NOS tubes can offer a bounty of sonic pleasure to those who choose to experiment with them and evolve their sonic palette to "recognize and appreciate" what they can offer. For some, NOS tubes are an acquired taste, for others they are instantly appreciated. And others still will not appreciate what NOS offers. No right or wrong in what you prefer.

(In today's production world, with tubes made in China and Russia, tube designations no longer strictly apply as was intended from the original production era.)

Here is a general evolution of the tube designations as I understand it. Of course these labels are for the original production tubes from about the 1950's - 1980's:

12AX7...
the original version of the tube. This can only be used in "parallel filament circuits only". Fortunately, this includes "most" guitar amps that we all are familiar with and the majority of audio gear...but there are some rare exceptions out there.

12AX7A... This version can be used in "series or parallel filament circuits". So no more limitation of "parallel filament circuits only".

ECC83... The European designation that is electronically equivalent to the 12AX7. IOW, the European substitute.

7025... The "low noise" version of the 12AX7. This tube has a spiral wound filament intended to reduce hum. Intended for industrial use such as for scientific, medical and hi end audio. In many guitar amps, such as a blackface Fender, some say they can here an extra sonic benefit; especially evident in the RCA manufactured 7025. I believe that I can easily appreciate the extra high end "sparkle" this tube offers in a Fender when used in the first gain stage. After you get used to hearing it you may not be satisfied with a stock 12AX7! Upon reading RCA tube manuals there is no claim made to an intended sonic distinction between 12AX7 and 7025; other than the intended goal of noise reduction. (The often noted sonic effect, the high end sparkle, is something that was appreciated by musician's and audio enthusiasts after the fact. Kind of an unintended, but highly desired, side effect of the subtle design change that was intended to function the same as a 12AX7A but with less hum.)

note...not all 7025 manufactured tubes exhibit the sparkle side effect to the same degree. All tubes vary in their sonic characteristics based on the plant they were manufactured in and the era of manufacture. For example, GE manufactured 7025's that I have used are just as quiet as RCA manufactured 7025 but have a bit less of the sparkle. This is because the GE tubes were made in the same era, but at very different manufacturing plants, than RCA tubes. The Amperex 7025 (a rare tube), still from the same era, is dead quiet but has less of the sparkle than the GE! Though Amperex tubes sound beautiful (my favorite tube overall) and are awesome in guitar amps. IMHO, the best sounding Amperex tubes for guitar amps were made in the 1960's in the Heerlen Holland plant. The location and era of manufacture is the key to understanding all tube sonics. The brands alone are not reliable indicators of the tube sonics.


12AX7WA... A version of the 12AX7 tubes made for the US Military. The W designates the "military" type designation. These tubes were were made with internal mechanical enhancements to make the tube more "physically" rugged. In short, a more "durable" tube.

A reliable place to purchase NOS tubes from the original era...including NOS Japanese production tubes which are very good alternatives for guitar amps, is Hi Test. I have known the owner, Gregg Levy, for many years and he always delivers quality NOS tubes at a fair price based on current market value.

https://www.hitestguitars.com/

There are other several online retailers of NOS tubes that are very worthy as well. Do your research on the seller before buying and choose wisely.
 
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slider313

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The 6681 was an industrial number for a "mobile rated" 12ax7a. This means it has a rugged filament to withstand many on/off cycles. Other mobile rated tubes were the 6679/12at7 and the 6680/12au7.

These tubes were found in old boat, police, fire dept and taxi cab communication systems; among others.

FYI; the power tubes that most of these radio's used were 6V6GT's.

I would stop at fire houses, if I was traveling through an old town, and ask if they had any of those old "radio tubes" laying around. This was back in the mid-late 70's. Most of the time the answer went something like,"Oh, we threw a couple of boxes of those in the dumpster some months back".
 
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King Fan

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We should put this thread back to sleep for another 10 years... maybe this is of those topics that improves with age, but it's too soon to tell. :)

OTOH, post #2 did kinda answer the question. I miss Scott...
 

BobbyZ

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Got a pair of Grove Tube labeled JJ 6L6s in some amp I bought. They're marked 6L6, 5881, and KT66.
That's how much the old tube designations mean with today's tubes.
On the other hand it's a pair of tubes you can put in a '59 Bassman, early JTM-45 or a Super Reverb and it'll sound exactly like the tubes that came with.
Or like alot like JJ 6L6. ;)
 

trxx

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Got a pair of Grove Tube labeled JJ 6L6s in some amp I bought. They're marked 6L6, 5881, and KT66.
That's how much the old tube designations mean with today's tubes.
On the other hand it's a pair of tubes you can put in a '59 Bassman, early JTM-45 or a Super Reverb and it'll sound exactly like the tubes that came with.
Or like alot like JJ 6L6. ;)

Who is making the best regarded 6L6 today? My super reverb came with an older pair of Mesa 6L6's which sound fine to me. I have a quad of RCA 6L6's in my twin, which I have yet to try a pair in my super. Wonder if I will notice any major difference. I already stole one of 7025's. I haven't noticed any major difference between that and more modern production tubes that I have on hand.
 

BobbyZ

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Who is making the best regarded 6L6 today? My super reverb came with an older pair of Mesa 6L6's which sound fine to me. I have a quad of RCA 6L6's in my twin, which I have yet to try a pair in my super. Wonder if I will notice any major difference. I already stole one of 7025's. I haven't noticed any major difference between that and more modern production tubes that I have on hand.

Good question and I wish I knew the answer!
I really haven't messed with many currently manufactured 6L6s. I need too because I'm out of old stock 6L6s and hate to spend the money on NOS.
Just keep in mind they're all made in three plants now, China, Slovinkia and Russia. No need to buy ones that are relabled and put into fancy boxes. Plenty of places test and match without all the BS you pay for these days.
 




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