The 1299A is an battery amplifier beam tetrode or beam pentode as the data-sheet says. This exhibit is marked as being made for the Canadian Westinghouse Company. As Sylvania introduced the Loctal base it is possible that they made this valve.
As an audio amplifier it can produce 0.6W.
The type designation is etched into the dome. The style is typical Sylvania.
Gettering obscures most of the glass but this image was taken from another 1299A.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B (Loctal) base pins, is 55 mm tall.
References: Datasheet & 1043. Type 1299A was first introduced in 1949.