The well know 651S1 HF receiver. This the very first model.
The PN522-4836-009 means it is revision 9.
- LED mods,
- Remote control,
- 444.5kHz reference.
The remote control DCU A9 card is not referenced but was made by Collins.
The 444.5kHz use is unknown.
The decimal point removed with the LED mods has been rewired.