What do the values stamped on these JJ 12AX7 represent?

[professormudd]

Greetings,

I was trying different 12AX7 tubes in on of my amps and noticed that 5 out of the 7 tubes (all JJ ECC83S) have very faint markings on the glass. Three of them say 23K1, one of them 14K0, and another 10J0.

Does anyone have any idea what these numbers represent?

For what it is worth, and I am sure this was a coincidence, but the 2 that didn't have these faint stamps were the quietest (least noisy) out of the lot and the three that say 23K1 are the noisiest.

[TUBEDUDE]

Tubes are usually marked with a date code and or factory code.

[bepone]

never seen that on ecc83 jj

[professormudd]

never seen that on ecc83 jj

What brands have you seen it on?

[professormudd]

Tubes are usually marked with a date code and or factory code.

That makes sense.... Perhaps it would be day, month, year? 23K1 being 23-November-2021?

[bepone]

never seen that on ecc83 jj

What brands have you seen it on?

never seen that on jj, but also not on others... there is a sea of fakes around... i know somebody was throwing on the market old ei factory scrap pcc189 for ecc88 , pcc was dirt cheap. who knows what is here..

[TUBEDUDE]

never seen that on ecc83 jj

What brands have you seen it on?

The British, Dutch and some Japanese made tubes.