I recently serviced the [auto-reversing + high speed dubbing + Dolby A&B] double cassette deck in my Sony MHC 5500 [new belts, lubrication, de-magnetisation etc.] .... and it sounds great! I now regularly set the timer to record a BBC concert [from the great FM tuner] and scoot off down the pub for an affable quaffable whilst it's doing its stuff!
P.S. The results also sound very good on/in my [Sony] Gamma OEM car headset too ......................