12AX7s-NOS RCA and Mullard differences

WhoJamFan

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Just curious to know if there is any difference between NOS Mullard and a RCA 12AX7 tubes-provided both are shining examples and work perfectly.
I see the trend of always recommending Mullards in British amps and RCA in USA amps, but is there any signifigant difference in the two, or is it more along the lines of what that amp originally shipped with at the time tubes were still mass produced?
 

Timbre Wolf

>thermionic<
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Yes - there are differences in sonic character.

To get specific, you'd first have to name the particular era/version of each tube you're comparing. Both RCA and Mullard/Blackburn had several versions of 12AX7/ECC83, each with their own character. But here's an example... comparing the '60's short-plate RCA 12AX7A to the short-plate Blackburn/Mullard ECC83 of the same time, the Mullard will provide you more harmonic-rich results, whereas the RCA will be relatively devoid of harmonic artifacts, giving you the unembellished fundamental tones. So blackface Fender cleans would be all the more clean using those short-plate RCA 12AX7A. There are also differences in tonal fingerprint, compression, clarity, and so on...

- Thom
 

hacinador

Member
Messages
764
Yes - there are differences in sonic character.

To get specific, you'd first have to name the particular era/version of each tube you're comparing. Both RCA and Mullard/Blackburn had several versions of 12AX7/ECC83, each with their own character. But here's an example... comparing the '60's short-plate RCA 12AX7A to the short-plate Blackburn/Mullard ECC83 of the same time, the Mullard will provide you more harmonic-rich results, whereas the RCA will be relatively devoid of harmonic artifacts, giving you the unembellished fundamental tones. So blackface Fender cleans would be all the more clean using those short-plate RCA 12AX7A. There are also differences in tonal fingerprint, compression, clarity, and so on...

- Thom
Thom, can you compare RCA long black plare D getter to Mullard short plate i63? I use RCA long plates in all my amps (british style - AC30, Orange, JTM45 etc.) and I love them. But I have not tried those Mullard short plates. Do I miss something? Thank you very much!
 

Timbre Wolf

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Thom, can you compare RCA long black plare D getter to Mullard short plate i63? I use RCA long plates in all my amps (british style - AC30, Orange, JTM45 etc.) and I love them. But I have not tried those Mullard short plates. Do I miss something? Thank you very much!
Sure - I'll try...

The '50s RCA long black-plate 12AX7 break up more easily than those I63 short-plate Mullard ECC83, and I'd say the RCA have greater clarity and slightly more frequency extension. The I63 tend to be more middy (especially lower-mids) in their character, even though the RCA also have a very thick/rich tonal character. Personally, I don't like the quality of breakup that those black-plate RCA exhibit - it is unique to them, and seems to me to be kind of a thick ripping quality (reaching for ways to describe), whereas the Mullards are more smooth and compressed in sound and feel. Finally, I've found that the RCAs are much more prone to microphony, so there is that to consider too (though you seem to have a good one). I'm much more enamored with earlier long-plate Mullard ECC83, so, if it were me enjoying the RCA, I'd advise sticking with what you already love, and leave the Mullards to others.

Hope this helps.

- Thom
 
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12,568
Can't vouch for long plate Mullards, which are probably a notch closer to the RCAs. Then the blackplate RCAs are a notch closer to the Mullard long plates, I hear, compared to the greyplates.

But I use a short plate 60s Mullard with 50s RCA long greyplates. The tubes are very different, almost opposites, like a tube screamer versus a Klon. The Mullards are all about mids, and the RCA's are all about this huge multifaceted sound with smooth breakup, and a certain 3D shimmer. The Mullards sounds smaller, but the mids are perfect for v1. Then I use RCAs everywhere else to restore size and 3D-ness.

The RCAs were too bright for v1, as a strat player. But they were smooth, and sounded great in their own way.

If anything the RCA's seemed, in a classical sense, to be a better tube. Full frequency response. Great lows and highs. Almost a chorusy shimmer.

But the Mullard fulfilled a specific valuable function, and I wouldn't want to be without it. I really needed those Mullard mids.

So I have combined them, where the RCAs are in v2 and v3.

With just the Mullard and stock new Chinese tubes, my amp sounded too small at low volumes. Not surprising given the mid emphasis. People have the same complaint about tube screamers.
 

hacinador

Member
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764
Sure - I'll try...

The '50s RCA long black-plate 12AX7 break up more easily than those I63 short-plate Mullard ECC83, and I'd say the RCA have greater clarity and slightly more frequency extension. The I63 tend to be more middy (especially lower-mids) in their character, even though the RCA also have a very thick/rich tonal character. Personally, I don't like the quality of breakup that those black-plate RCA exhibit - it is unique to them, and seems to me to be kind of a thick ripping quality (reaching for ways to describe), whereas the Mullards are more smooth and compressed in sound and feel. Finally, I've found that the RCAs are much more prone to microphony, so there is that to consider too (though you seem to have a good one). I'm much more enamored with earlier long-plate Mullard ECC83, so, if it were me enjoying the RCA, I'd advise sticking with what you already love, and leave the Mullards to others.

Hope this helps.

- Thom
Thank you very much for such a great post! I have a dozen of those RCA Black long plate 12ax7, I use them in everything and in every circuits possition. I like their clarity and somewhat breakup. They have nice piano like sound when they are clean and when they are overdriven then their breakup is somewhat aggresive, but I still pleasant for me.

But I really must try those short plate Mullards. I will buy one or two.
 

earthmud

Silver Supporting Member
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3,764
I have Mullard i61 AND i63 short plates in v1 and v2 of my Crossroads but for the v3 PI position a RCA short grey plate was the winner. I compared RCA long black plates and Sylvania long black plates but there's something about the RCA short grey plate that sounded best in the PI position. In my JMJ30 I have a Mullard long plate mc1 in v1 and Mullard short plates in v2 and v3.
 

CallEOD

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2,104
I tried Mullard in a Fender Twin and it really wasn't much of a change, sounded better with Sylvanias.

Conversely old Marshalls really shine with old Mullards.

So do Raytheons but they're like $350 bucks a piece.
 

teleman1

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16,218
I can't even come close to as good a description as Thom laid down. But I will say in past dumb guy comparing that when I roll tubes, Mullard wins. I hear a Bugle Boy, sounds nice, RCA in a Fender amp, hmmm. But when I have challenge any tube with a Mullard; Mullard wins. It always seems to have something more than the other tubes. Whether appropriate for the sound or not. Telefunkens sound nice for cleans, but I have like RCA's better. My mindset on Telefunkens is they better serve in the audiophile arena. To sum it up, I find it easier to say, there's is nothing not to like about a Mullard. When things are critical for someone, like a bright amp, speakers, circuit, I always lean on Thom cause he is dang spot on the money. Whereas me, I just offered a generalization of my feelings. And cost has a lot to do with it and ANOS offers many to experience what OLD stock is all about.
 

northfortyrecords

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1,348
In my experience (and speaking in very general terms), my RCA AX7's have very nice and precise cleans in my Fender style amps - almost perfect, but they overdrive in sort of a thuddy way in the lows, with too much fizz on top.

My Mullards are incredibly rich in harmonics, lush even, when clean and still plenty clear. Not exactly the same wide soundstage as the RCA's, but super nice. When they overdrive, they just keep getting more complex and lush.

Both are some of the best vintage tubes you could come across.
 

Timbre Wolf

>thermionic<
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12,305
I have Mullard i61 AND i63 short plates in v1 and v2 of my Crossroads but for the v3 PI position a RCA short grey plate was the winner. I compared RCA long black plates and Sylvania long black plates but there's something about the RCA short grey plate that sounded best in the PI position. In my JMJ30 I have a Mullard long plate mc1 in v1 and Mullard short plates in v2 and v3.
There's so much I like about this post - first, I've been admiring the Crossroads quite a bit. Quite! But the fact that you've taken these legendary tubes through the paces, listened critically, and selected based upon what you hear/feel, rather than "reputation"... that's cool!!
 

Timbre Wolf

>thermionic<
Platinum Supporting Member
Messages
12,305
In my experience (and speaking in very general terms), my RCA AX7's have very nice and precise cleans in my Fender style amps - almost perfect, but they overdrive in sort of a thuddy way in the lows, with too much fizz on top.

My Mullards are incredibly rich in harmonics, lush even, when clean and still plenty clear. Not exactly the same wide soundstage as the RCA's, but super nice. When they overdrive, they just keep getting more complex and lush.

Both are some of the best vintage tubes you could come across.
Yes - we have similar experiences! I find the short-plate RCA 12AX7A to have really, REALLY fat lows, with bright highs. BF "scoop" character and reputation is accentuated by this classic valve.
 

earthmud

Silver Supporting Member
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3,764
There's so much I like about this post - first, I've been admiring the Crossroads quite a bit. Quite! But the fact that you've taken these legendary tubes through the paces, listened critically, and selected based upon what you hear/feel, rather than "reputation"... that's cool!!
Thanks! I love my Crossroads. To make it even better I have Amperex D getter rx3 EL84's and a Mullard D getter ez81 in the Crossroads as well. I learned about those from reading your posts so a huge thanks to you!
 

Timbre Wolf

>thermionic<
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12,305
Thanks! I love my Crossroads. To make it even better I have Amperex D getter rx3 EL84's and a Mullard D getter ez81 in the Crossroads as well. I learned about those from reading your posts so a huge thanks to you!
Wonderful! Wow - I'd really love to hear that!!
- Thom
 

Fulldrive-1

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5,926
When you're pushing your signal through a fuzz and a Univibe, into cranked Marshalls, you'll never know the difference.
 

lostpoet2

Silver Supporting Member
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3,318
from Brent Jessee's page: http://www.audiotubes.com/12ax7.htm

Mullard "When it comes to warmth, no other tube can top this jewel from the British crown. Silky highs, a liquid midrange, and awesome deep bass give this tube its deserved reputation for warmth and full sonics."

RCA "The RCA is the King of rock and roll tubes, without equal. From their throaty growl in 1960s guitar amps, to the sparkle and warmth of the blackplates in a hi-fi, these tubes have it all. Warmth approaching that of the Mullard, this tube is truly a Jack-of-all-Trades and at home in almost any application."

Personally, Iusually shop for value, and I look for American made JAN long gray plates and misc. brand (but made by RCA) blackplate and 12ax7s. Don't be afraid to buy used tubes that have been tested on a calibrated tester.
 




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