Tungsram Valve date codes

Also FYI , taken from a Hungarian old tube website

Zeitmann Tubes

There are three modes of labeling of Tungsram tubes:

-marking with yellow colour means: tube for common use,
-marking with red colour means: tube for industrial use,
-marking with yellow or red colours plus letters
"HM" or "HONVEDSEG" means : tube for military use.

Tubes marking with yellow labels got into shop keeping networks.

Red labeled tubes were manufactured for industry.
Each of them were made quality tests.
You can regularly found serial numbers on their bulb.
Five thousands or maximum ten thousands were made of them in types.
So therefore they are rather rare ones.
Industrial tubes had been burned for minimum 50 hours.

Military tubes absolutely have been selected for army.
These tubes were assorted by strictest requirements and test results.
Then were labeled by military sign/code stamp.
Tests were always made in an assistance of an army assign.
They are very rare tubes, and we can correctly say only
our depot contains so devices( several tens in items).
Each of military tubes had been burned for 200 hours.