The Mullard tubes in my Heathkit WA-P2 preamplifier were made in Great Britain, types 12AX7 (ECC83) and 12AU7 (ECC82).

They have the code 1.4.7 stamped on their backs. Is this a date code?

Thanks!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I'm not a huge fan of the Audiophile that permeates this site, but, here's a link to a rather ambiguous description of these highly ambiguous codes:

http://www.audiotubes.com/mullcode.htm

Thanks, I did look at that reference before posting here. It lists nothing like these codes.

I don't care about them for Audiophile reasons. I'm just curious whether these might the original tubes. They test like new and the preamp is one of those time capsules that looks like it was built and never really used.

Phil Nelson

Those black acid etched letters that are visible on the back side of the tube (the side without the Mullard logo) are the codes that will tell you the date/month of manufacture.

If you post them here (I can't really make them out), I will be able to decipher the coding.

Oh, hello! I see the BIG white ink numbers now.
Had to look at it with my new eyes! I have no clue as to what those mean.
My SWAG: house date code or evidence of screening for a bulk purchaser.

"1.4.7" is not a date code. The one I can read is "B7D", which is April 1957. I suspect they are all similar.

Jim Cross

Good call since the pre-amp is from around 1957 as well, that would make sense rather than 1967. The B is the Mullard Blackburn factory.

Frank

Aha -- I didn't notice the little black characters. The 12AU7 says k61/B7C, the 12AX7s say mC1/B7D.

So, I guess that means March and April, 1957?

Phil Nelson

I think you are right on.
k6=ecc82 and mC=ecc83 the 1's indicate the original first internal construction.

Frank

Don't touch the decals, they will come off and cut value by 90%. If the filaments are good and no shorts, someone will scoop them up at foolery rates regardless of manufacture date, but if not, target practice.