Mullard cv4003 & 12au7 Blackburn

As a beginner I'm trying to understand the differences here. The Blackburn made ones I think were made in the 60's and the cv4003 during the 80's? What sonic differences, if any, are there?
msummers, 12AU7 and CV4003 are two different names for the same tube. 12AU7 is the American designation and CV4003 is the British designation. ECC82 is the European designation. There are also many variations with other names, such as the Amperex 7316 or the Mullard M8136, that are basically the same tube.

Most Mullards were made at the Blackburn plant, with the Mitcham plant coming in second. Tubes made at other Phillips factories were often labelled Mullard, though.

Brent Jessee has a lot of information about tubes on his website:, including how to read Phillips tube codes (see the yellow box entitled "Euro Tube Codes"), which will tell you where and when your tube was made, whatever it is labelled.

Check out his website and if you have more questions, which you probably will, feel free to ask. I would start out by reading up on the 12AU7 by clicking on the the yellow box with that title.
I spoke with Andy at Vintage Tube at length regarding Mullard, since I was looking for the very best, most holographic tube that Mullard offered. He stated that the ECC82/12au7 Boxplate and the Longplate O-Getter 1950's had the finest sonics and measured as lowest noise.

The CV4003, also Blackburn, is not as extended and he thinks is a lesser grade tube; (1970's). Kevin at Upscale disagrees.
Google Joe's Tube Lore and read his findings after testing many brands and tube types.

In addition, Brimar has similar sonics to Mullard...warm, liquid mids and a smooth top-end. I have various 1950's Mullard Longplates, the low noise sound exceptional.
But I found that the Brimar CV4003 have excellent depth, and upper and lower extension.
Edit...My bad, in looking thru my notes, it is the cv4004/12AX7 that Andy said was a lower grade Mullard. The CV4003 is a military spec box plate.
Because of this thread I called Andy and my order got a little out of hand!

I found him straight to the point and his reputation is that he can be very trusted. After chatting with him and asking opinions and such, this seems to be the case. Also from reading around here (and elsewhere) it might be awhile until I get the tubes but can hope sooner or later. I know he tests everything quite thoroughly, matches and the order I have is quite large.

Prices on his website need to be updated though.

Ended up with:
2 NOS Mullard rectifiers
6 NOS Mullard 12AU7/1960s (1950s too much for me)
6 NOS RCA Cleartops 12AU7

Shipping was pretty reasonable to Canada. Will report back once I've played around with them for awhile.
@msommers , well done. And it seems like his prices are only a rough number for the price of tubes. The price changes with the quality of the tube (how well it tests).

A couple of questions for you...
- What gear are you using?
- Why did you need all Mullard? Different amp/preamp stages can use mixed brands of tubes.
I'm using the Primaluna Dialogue Premium preamp.

This only has 4/6 gain tubes so I should of stopped there. But I asked him what he thought if the cathode followers were worthwhile to change out. He didn't know what the Primaluna stock brand tubes were but guessed they were modern-issues from Russia, China or Czech Republic. I don't know if anyone knows what PL's rebranded stock tubes actually are. His opinion, very boldly so, was that they're all crap in comparison to the older ones and won't last as long either. I kinda took this with a grain of salt but decided to go for it anyways because I'd wonder. In the end if the cathode follower tubes don't change anything, it wasn't a huge expense and if anything they'll last quite a few years.

Regardless for my setup, the highs were too shrill and the mids a little recessed. He said the Mullards would be a good match for this as they're the darkest tonally he has with a rich and lush midrange, with the RCAs second slightly more towards neutral. The Tele's Tungsols and Amperex were neutral to airier/detailed/forward.

I will mix and match between the sockets and see if there is any combo that sounds the best. Mullards have such a following that I gotta try them :)
the highs were too shrill and the mids a little recessed.
I've been there. Mullards are the way to go. The cathode follower does influence the overall sonic signature, but less than the front tube, of course.
I've used Mullards for gain and RCA Cleartops as followers. You get the Mullard sonic signature with some air at the top-end.

Let us know how it turns out.
Oh yeah, what did Andy say about the CV4003 tube?
I think the Primaluna stock tubes are made by Shuguang for PL.  

I've tried a ton of preamp tubes in my PL Dialogue Prem. HP integrated.  I like Ciftes, Mullards, GE military spec.  RCA clear tops are really bold and aggressive, which is fun but a bit too forward for me.  I sometimes mix a couple cleartops with Mullards or Ciftes with Mullards. 
@lowrider57 I actually forgot all about it haha. Guess it doesn't matter now. The price was way less than Upscale Audio's $110USD CV4003 and I'm sure 60's Blackburn Mullards were quality.

Mixing tubes sounds like a good way to go. Thanks gents!
Good deal, @msommers . I've bought from Andy four times and all his tubes have been of outstanding quality.
msommers, Perhaps I shouldn't write this, since you've already spent your money, but IMO the best sounding 12AU7/ECC82/CV4003 is actually a 6CG7 (in 9-pin miniature format) or a 6SN7 (octal base).  Neither of these tubes is in the 12AU7 family but both of them exhibit the electrical characteristics of a 12AU7 and can be substituted, if you know what you're doing with the tube socket.  You just have to fiddle with the filament connections vis a vis the 6CG7/6FQ7. 6SN7 would take a lot of work and probably is not an option.

Amperex 7316 is not exactly a 12AU7 but can be installed into the same socket with no mods and is close enough electrically that there are no problems.  Nice tube, too.  I admit I have a bias; I have never liked the 12AU7 in a gain stage. OK for driver or phase splitter.  If one must, I liked the Amperex Bugleboy Ecc82/12AU7 best amongst a bunch of others I tried in a gain stage, back about a decade or more ago.  Real Bugleboys are scarce now, sadly.
It's no problem honestly. I bought these knowing full well that I might not even like them! Such as it goes in this hobby. I figure with a reptuation like Andy if I got to sell them at least people can know it wasn't from some random person. I'm not much into tinkering with sockets and such anyways. 

What I was really after were Brimar 13D5 (lots on eBay from India!). Apparently Brimar CV4043 are the better version according to a seller on eBay, which might be true, but I actually looked through various documentation available for CV4003 and CV4043 and nothing came back that they were compatible, even trying to decipher datasheets. I'm a complete amateur so I might be out of line but something just didn't seem right.
In the event someone comes along looking for 13D5 info, I asked Brent from Brent Jessee Recordings about this and his thorough, gracious answer was:

"The 13D5 is one of the best British 12AU7 tubes ever made. It was designed from the ground up to be low noise, uniform output, and long life. The CV4043 is a military version of the industrial 6061, which is not compatible with the 12AU7 and is not a recommended substitute.


CV tubes are British military spec tubes. They are not designed for audio use but often are very good tubes because they were built to withstand impact and vibration. The 13D5 is still a superior tube. We have them in stock. They are listed on our 12AU7 page if you are interested in singles or pairs."

Even for just four I think they're beyond my budget for such a thing but they could be the best for anyone else looking.