The 12BY7A is a 1950s video amplifier output valve designed for boosting wideband TV video signals to a sufficiently high level to be transmitted over a considerable length of cable without loss of quality.
This valve is labelled as being supplied by Tektronix and we can infer that the 12BY7A was selected for the stringent requirements of Y amplifier service in Tektronix oscilloscopes.
The heater is rated for 12.6 volt use and is centre tapped.
The Tektronix part number.
The anode on the left with the beam plate visible in the centre.
Looking along the grid axis through the end of the beam plate. The screen grid is wound on copper supports. Both grids pass flat across the cathode as can be seen just above the lower mica.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 59 mm tall.
References: Data-sheet, 1040 & Henning Hertz. Type 12BY7A was first introduced in 1955. See also1955 adverts.
