The CRT used in the Tektronix 535 is part number 154-081. It is a 5BGP2, which Sylvania made. It also goes by the Tektronix designation "T51P2A".
The 5BGP series from Sylvania is a 5-inch CRT that was available with a variety of phosphors including P1, P2, P5, P7, P11, and P15.