(slightly microphonic tube) 12AT7 Brimar UK black plates "D" getter halo copper grid posts used/good 1955 era (7.2/8.4ma)

slightly microphonic tube) 12AT7 Brimar UK black plates "D" getter halo copper grid posts used/good 1955 era in white box

7.2ma Gm=4300

8.4ma Gm=4600

- microphonics only noticeable when tapping on tube

- recommended as driver or buffer tube