These are geniuine Philips ECC81 12AT7, Made in Herlen, Holland, flat foil crossbar D getter, single plate hole and Tk1 delta 0A codes. Made in 1960 in Herlen tube plant
It’s also possible to find them labeled Amperex Bugle boy 12AT7 ECC81
No side holes in plates, Tk1 Δ0A Heerlen code is clearly visible on 1st photo.
These tubes are used, but tested 90-105%. Here is shown perfectly matched quad.
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