I want to say the same.

O.K. in TenFourFox (PowerPC Macintosh, OS X 10.4.11).

(Safari 4.1.3 can't open ql-forum at all.)

I'm interested in 4) - the QIMI board.

You can
1) press ALT+TAB to switch screens manually,

2) MODE 96,-1 - see https://superbasic-manual.readthedocs.io/en/latest/M/mode.html

I do not have schematics for the Miracle interface, but I have some files from ing, Louis Seidelmann for his new (2015) interface. He has 4800 and 9600 baud version of this. About the Sandy interface (probably confused with Miracle?) he said, that it uses clever solution "using shift register a...

File header on the beginning of the file?

I think the comment stated the River Forth...

I have found two Forth villages in Scotland (not very close to Forth River) and in Germany (part of Eckental).

Yes, it is. But remember, that Russian clones have stronger output for SAVE, than original Ferranti ULA. ZX Taper read ssignals from 1 V up. https://translate.google.com/translate?sl=auto&tl=en&u=http%3A%2F%2Foldcomp.cz%2Fviewtopic.php%3Ff%3D39%26t%3D3597%26hilit%3Dtaper%26start%3D75%23p44350

Unfortunately, we need only mass production ( big batch ) for QL case to have the resonable price.

Can be the ZX Spectrum Next case used for QL/Q68 board?
That is mass produced, and we can try some negotiation about suprlus production for QL use.

I cant remember whether or not WHEN ERRor is part of SuperBASIC QL ROM (post JM) This SuperBASIC structure does not work very reliably on any QL versions other than Minerva v1.77 (or later), SMS or the THOR XVI: although Toolkit II improves the reliability... https://superbasic-manual.readthedocs.i...