Back in 1984 I wrote some games for Spectrum - Will they still be playable?

In regards to "is there a way to play my old games again?", there is a good chance that they are available online somewhere. You might start with the Internet Archive.

Collectors and enthusiasts have already made archive copies of almost all spectrum software so if your games were ever on sale there is an excellent chance that someone has already preserved them and you can play them via an emulator.

Back in the '80s, I wrote a couple of games too. A few years ago I have found the old cassettes with those games, but I had no tape deck at all. I bought a "USB walkman" Basetech BT-USB-TAPE-100 on eBay for a few dollars. Then I just plugged this deck to my PC and record my old tapes to uncompressed WAV (at full possible sample speed, 48 kHz, 16 bit, stereo). Then I have cut them using Audacity and converted to TZX via some utility (named WAV2TZX or so...)

I was afraid that those old cassettes will be unreadable and the sound record will be damaged, but I was surprisingly successful. So - try it, it can be done.

Yes, quite possibly. Unless the tape is damaged with complete dropouts, I would be cautiously optimistic that you can recover it. While ageing tends to increase wow/flutter, and can cause the recording to "fade" for lack of a better word, complete drop-out is uncommon unless the tape is actually disintegrating, or the oxide is flaking off.

There are also some techniques, ranging from using a simple audio filter, all the way to actually squinting at a waveform of the audio to guess whether a bit is supposed to be 0 or 1, that make it more likely you can recover it even if a Speccy wouldn't be able to read it.

I would try to secure a good quality digital recording of the tape, ideally FLAC or WAVE lossless. Perhaps you know someone who has an old stereo with a tape deck in a dusty storage room they've forgotten about? (Oh, do make sure it works with a sacrificial tape first!)

well, if you really want those games back, just buy the tape.

Then buy a cassette player (they're cheap, you can try to get a high quality one) or find a friend who still has one. Now:

• Make sure to clean up the player heads with isopropyl alcohool before using it.
• Rewind the tape
• Extract it and use 2 pencils on the reels to gently tighten the tape so it's not loose. Loose tapes have a tendency to unwind in the tape player. You don't want that. Be gentle! Don't break the tape.

Then digitize the output using audacity (some steps will be similar as this Q&A: How do I extract the program from the Radiohead "Nude" tribute by James Houston?)

There are converters that can convert wav to tap format (TZX is an alternative) for emulators, or emulators that can load directly from .wav or even from the real tape (but digitizing allows to give back the tape player that you borrowed).

Then you can try to load the converted file. If your program is in assembly, just dump the code to a file and use a modern disassembler to get it back (without symbols or comments, that's the problem).

On the other hand, if your programs are in BASIC, you can read your code again using the emulator, print it, or even convert the BASIC program to plain text (there are tools for that, like listbasic, from the fuse-emulator-utils Debian package: Make a BASIC TAP file readable on Linux)

The only gamble you're taking is that by buying a 36-year old tape you're not sure at all if you can recover all data from it. But even if there are errors, they can be fixed afterwards (specially with a BASIC program).

I remember doing this very operation for a lot of my Oric tapes, that was in 1996, so it's been a while. But most .TAP files that can be found on the Oric nowadays originate from those conversions.