Arrival
My HP 9825A arrived from France 
Whether it works or not is unknown. It arrived in good but dusty state, but the tape drive is missing sadly enough.
The markings say it is a 9825A which is most probably correct; it has the System ROM cartridge that should no longer exist on the B.
Device pictures:
Opening up showed the following:
The keyboard and printer assembly:
The device has clearly been opened before and was left in a non operable state: screws were missing, the cables to the cassette were left dangerously loose, and the keyboard assembly was not connected.
Board overview
The topmost board is the RAM board. The slot above it is free and empty. The board has number 09825-66523 rev B, supposedly a 16KB RAM card:
After removal of the RAM board, by moving it to a 90% angle and then sliding it out of its hinges by moving it sideways, we see the cassette board:
A detailed picture of it after removal:
