Make a "tape" file and save my BASIC program to it. How?

[vlig]

Hello. I just want to experiment with Spectrum 48k BASIC and to save my work to a new blank "tape", as in native case. Then to try it in other Android emulators, share it to PC or even maybe to a live old good device. Recording here starts to write to a .rzx file, which obviously isn't the desired way, especially given the fact of the well-known colons-in-the-filename error. I tried to save my stuff to a copy of a .tap file with some game in it and once it have worked out to the end of a tape. But it's impossible for me to repeat the success by some reason...