Amperex ECC83/12AX7 tubes.

Trying to identify what these codes mean on some Amperex ECC83/12AX7 tubes that I have.
They are 'Bugle Boy' type, made in Holland, and these are the codes:

59 UU

I 61 49G


Thanks,
Frank.

I'll take a shot at the second sequence I61 49G. Not sure what the 1 is doing in that sequence.

If it were I6 49G it would be:

I6 = Amperex (also known as Philips) designation for 12AX7 (also known as ECC83)

4 = Made in Heerlen, Holland ( the 4 is actually a right triangle symbol)

9 = 1959 (year of manufacture)

G = July (month of manufacture)

Regards,
Wayne

Thank you! That's very helpful info for me!

Frank.