Hi, as an alternative, here is my 2519 replacement with narrow HEF4557BT:
These are available at low cost in China or from utsource.
By using the 3.9 mm narrow version and 0603, I was able to place all components on the underside and minimise the size of the board.
Optionally, you can install a power LED or a bottom LED.
Installation under the Apple 1 board should also be possible.
The 2519 replacement has been tested in the Apple 1 board with real Charrom, standard and LS-TTLs.
Github: https://github.com/vossi1/Apple1-2519-replacement?
Christian
