I've said it before and I'll say it again.....back in the 70s and early 80s people got really creative with their machines! In those days if you needed a new peripheral or circuit board and one wasn't available you designed and built it yourself. Take this one - a humble singleboard Microtan65 that's been lovingly enhanced by its owner, first by adding the TANEX ROM/RAM/serial expansion on a twin-slot backplane and then an external and apparently rare TUG Board E.S.C that had been produced by the Tangerine User Group to add a load of extra ROMs. Of course, it HAD to be external since there wasn't space inside that solid wooden box for a 3 slot backplane :) Also, the only options available were 2-slot and 12-slot.

The E.S.C (EPROM Storage Card) could hold up to 16 2716 ROMs and is controlled by a pair of 6821 PIA chips. Unfortunately there's zero documentation for the ESC but there IS for the followup board, which was called the ESC COMBO. The manual gives each ROM slot's address so here's what's in my ESC:

Each ROM is loaded into RAM by a routine at $EFFC so to load it you type GEFFC and the routine asks for ROM start address, length and RAM location to write to, so to load Invaders you'd type:

The machine will respond with EFFF meaning it's loaded, so to start the code you'd type G400. Instant Invaders, in this case.

There's also a blinkenlights panel connected to a serial port and 2 more ports taking up the EPROM burner you can see in the pix - 3 9V batteries required! Finally there's a choice of either the original Tangerine hex keypad or a nicely cased 'real' keyboard that's been nicked from an original Bell&Howell Apple ][....

(For my ultimate in homebrew machines have a look at the Ohio Superboard at the bottom of this page)

I took some new pics prior to the 2022 RetroFest at the Centre For Computing History in Cambridge UK