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?
msommers
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.