ga is the tube type and 7 is the change code. So the important part here is that the tube is an ECC88 military type. The next line is the factory code followed by the year, month and week of manufacture (usually).
If the "4" is actually a triangle, the tube was made at the Phillips factory in Heerlen. A true 4 I believe is Phillips Eindhoven.
The last string of characters probably indicates year 2, month November, and week 3. My guess is it was made in the third week of November, 1962.
Warning: I've seen several tube code standards, so I could be wrong!!!
PS - ECC88 = 6DJ8 = 6922
