The small volume batch production of modern valve manufacture has a consequence of a greater spread of characteristics than used to be the case in the past with high volume production runs. Groove Tube, and other manufacturers, test the production and separate the output into different classes. With Groove Tube the classes are yellow (low), orange (medium) and red (high). The ratings are for their use in guitar amplifiers.
Groove Tube is an American company, San Fernando, Califonia, but this valve was made in Russia.
The Made in Russia lettering.
The expected oval anode of the 6V6.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 70 mm tall.
