I also looked for boombox cassette players they are all chinese, Quality products are obsolete now.
Even those 3 or 5 CD changers Mini HI-fi by sony , LG all gone. Now they 're manufacturing these stupid looking portable single unit party speakers and soundbars.
yes, I do own one of these Panasonic SC-UA7 (sounds very good) but when audio is recorded in stereo wtf will these portable boxes do.
My 90s music system worked for almost 16-17 years and I still got many hindi english cassettes, but same like you, these cassettes are all 20+ yr old now. some are even 30+ years.
Cassettes sound more organic, kind or juicier or addictive.
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Nothing special we can do for these cassettes, best we can do is to keep playing them and store in dry and cool place avoiding the only enemy (moisture).