Blonder Tongue AB800 A/B Pin Diode Switch for Video All-Call System ( RMD P/N 014-0800 ). Blonder Tongue AB-800 Pin Diode Switch for the Video All-Call System. Blonder Tongue Video All-Call System provides an integrated solution of allowing one channel to override all other channels on all televisions, such as in a school system. In order to integrate all of these components into a complete all-call system, Blonder Tongue also offers the Distribution Amplifier and the AB-800 Pin Diode Switch. These two products are used to distribute the alternate audio/video program to each modulator and processor in the system. When invoked, the substitute IF program will override the normal IF programs available at each modulator and processor. Every channel in the system will be overridden with the new program. This product is designed to be used with the Video All-Call Distribution Amplifier.