Original RCA 7025 and 12AX7 preamp tubes

Figaro

Silver Supporting Member
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12,983
The original RCA 7025 seems to be the favorite preamp tube of many players.

How many different versions of the RCA 7025 are there?

Which current production 12AX7 sounds the closest to the RCA 7025?

What about the original RCA 12AX7? How does it's sound compare to the RCA 7025? How many different versions of the RCA 12AX7 are there?
 

Blue Strat

Member
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30,194
For the RCA 7025s, there are at least a long gray plate, long black plate and short gray plate. That's all I can remember seeing.

For the RCA 12AX7, there were long gray and black plates. For RCA 12AX7A there are short gray plates.

Nothing new sounds like an old RCA 7025.
 

Figaro

Silver Supporting Member
Messages
12,983
For the RCA 7025s, there are at least a long gray plate, long black plate and short gray plate. That's all I can remember seeing.

For the RCA 12AX7, there were long gray and black plates. For RCA 12AX7A there are short gray plates.

Nothing new sounds like an old RCA 7025.
Thanks, which new 12AX7 sounds the closest in your opinion?
 

FattMetheny

Active Member
Messages
85
Thanks, which new 12AX7 sounds the closest in your opinion?
I tend to like short plate versions of RCA, GE and Sylvania. Long plate tubes are more likely to become microphonic at high gain.

Low(er) gain folks tend to appreciate the long plate 12AX7s.
 

Blue Strat

Member
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30,194
Thanks, which new 12AX7 sounds the closest in your opinion?

Sorry, I'm not going there. Last time I did that I had an irate customer on my hands. He coerced me into recommending something close to a tube he loved after I told him to stick to what he knows he likes.

Best advice? Try everything you haven't tried already. It's the ONLY way to know. You'll probably end up spending more money on shipping then you would on the tube you already know you love.
 

Timbre Wolf

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How many different versions of the RCA 7025 are there?
At least 3: the short gray-plate is the most common, so I'll assume you're referring to it. Long gray-plate and long black-plate 7025 also were produced in the late-'50s

Which current production 12AX7 sounds the closest to the RCA 7025?
None - by a long shot.

What about the original RCA 12AX7? How does it's sound compare to the RCA 7025?
Comparing the mid-'50s long black-plate RCA 12AX7 (not the original that RCA first made in 1947) to the short gray-plate 7025: the long black-plate breaks up earlier, has thicker mids and lows, the short gray-plate 7025 has tighter lows, chimier upper-mids, and breaks up relatively later.

I'm aware of these RCA 12AX7 types:

late-'40s semigloss long black-plate 12AX7
'50s long black-plate 12AX7
long black-plate 7025
long gray-plate 12AX7
long gray-plate 7025
short gray-plate 7025
short gray-plate 12AX7A

There may be others...

- Thom
 

Blue Strat

Member
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30,194
Just thought of another version of "RCA" 7025. Later in the game, 1970's, RCA sold Sylvania 7025s labeled and boxed as their own.

Make sure you know which version you like.
 

Trout

Member
Messages
7,550
The original RCA 7025 seems to be the favorite preamp tube of many players.

How many different versions of the RCA 7025 are there?

Which current production 12AX7 sounds the closest to the RCA 7025?

What about the original RCA 12AX7? How does it's sound compare to the RCA 7025? How many different versions of the RCA 12AX7 are there?

Not sure which current production 7025 sounds closest to the original but in A-B-C tube rolling here, the TAD Select 7025WA has easily won out on every set of ears I have exposed them with.

I love them as well.
 

Timbre Wolf

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Just thought of another version of "RCA" 7025. Later in the game, 1970's, RCA sold Sylvania 7025s labeled and boxed as their own.
That would be a re-brand.

But it is a good point to gain as much certainty about the true identity, especially if you want to try to get another just like it.

- T
 

Figaro

Silver Supporting Member
Messages
12,983
Here are some 7025s from my stash. I picked these because they are all marked differently. The first one from the left is not an RCA. It is marked 12AX7, 7025, Fender and made in the USA. The other three are RCA. The 3rd one has long plates and is marked Made in Yugolavia. They all have grey plates. Any info on these appreciated!

 

cap47

Member
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2,273
EI was a common tube rebranded RCA with smooth plates from Yugoslavia. Good sounding if you found one that wasn't micro!
 

Timbre Wolf

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Here are some 7025s from my stash.
The one on the left is a GE; you can tell by the unique mica disc notches.

The two with flat-cut mica disks are RCA

The "RCA" long-plate is Ei. It is not really a "7025", but has been painted as if it were.

- Thom
 

Timbre Wolf

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These two RCAs have different 7025 markings. Do you know if that means they are from different years?
I noticed the stencil font, which is unusual. But I don't know what years those two samples were made. Gaps in the octagon will indicate production time. It takes skill I don't possess to decipher that information.

- T
 

DaveKS

Member
Messages
16,704
These two RCAs have different 7025 markings. Do you know if that means they are from different years?
Well if you can still read the 2 letter code you can date them. See page 18 of this. https://www.dropbox.com/s/fshy4welx3d7ckr/RCA DATE CODES.pdf
Think I read BD on right tube which would be July 66'.

Here's another relabel, RCA painted on glass.


100% tungsol construction inside though.


Tube monger can be a great place for learning internals of various makers. Here same TS tube on right.
http://www.tubemongerlib.com/galler...60+Long+Plates+Square+Getter+2+-+USA.jpg.html
 

Carl_Tone

Member
Messages
6,087
I bought a couple of mullard shortplates on ebay and for a 'bonus' the guy thru in a perfectly good short grey RCA 7025 and a RFT.

When I put that RCA in Vi and a long plate mullard in V2 a short grey RCA in V3 and a chinese gt pi tube along with Sylvania 6L6s...my amp never sounded better.

This particular amp really needs those old tube to shine. My cheap Pignose 60? Not so much. It sounds great with GT 6L6 GEs and GT-STR-12Ax7 R3's

I even threw a few of my good tube in it and figured the difference wasn't worth it.

If you want a modern tube close to that good...probably not happening. I'm really glad someone sent me one though. I already got it a back up.

I hear the Gold Lions are pretty good but they cost almost as much as anos and won't last.
 




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