Hint: Due to the high gm of the D3a, a conventional measurement with a tube tester is not possible. At least not meaningful.
Only a measurement in autobias mode is reliable


1 x  pair D3a Siemens tubes

3-mica quality

Can be used for any: 7721 5A/185K

Datecode inside metal label: X6 8H + 9J

Tested with RoeTest in triode mode:
Test result: gm = 25 + 26mA/V which is good

Random samples were taken for noise. No abnormalities