Looking for Input from Mullard Experts

[DeadWax]

I have a pair of Mullard branded CV4004 / M8137 (12AX7) box plates as shown in the photo below. The date code is R3D1 which I believe means they were made at the Mitcham facility either in April 1963 or April 1973. I'm not knowledgeable enough to know which date the shield style and/or internal construction matches best. Thoughts from the resident vintage tube experts would be greatly appreciated!

 

[Argonaut]

Whilst I am No expert they look like early 70’s production to me.

 

[DeadWax]

Whilst I am No expert they look like early 70’s production to me.

Yes, I believe so as well. Among other features, I believe the 1963 production may have indicated "Made in Gt. Britain" on the glass...as opposed to "Great Britain"

 

[Lowrider75]

Whilst I am No expert they look like early 70’s production to me.

I don't recall seeing a 1960s Mullard with 12AX7 lettering. They both should have CV4004 on the glass. So I assume later production.
Boxplates are fantastic sounding tubes.

 

[Chop]

I have some 8137's. I think those are 70's production.

 

[Argonaut]

I have some 8137's. I think those are 70's production.

Fine valves , I have managed to acquire a few boxed NOS over the years

 

[Big Dog RJ]

Roger that!
The Mullard M8080/ CV4058, one of my favourite input tubes of all time! Used in many of CJ's power amplifiers as the input gain stage, the musicality in these is just superb! Many designs have switched over to the 6922 / E88CC tubes, dual triodes. Having these same tubes with pretty much the exact specs, operating in the same input/ driver stage circuits, probably offers a better sense of balance and overall a more neutral performance but when listening to a Mullard M8080, boy does it get so engaging.
Marvellous combination!

Cheers and big woof!
RJ