Try cleaning your Tape Heads......they get clogged with Oxides off the Tape....
and or De-Magnetize the heads on the Tape Deck......Also Tapes do get damaged by being placed close to SPEAKER magnets...! If you do Gigs in various places, then
its quite likely to occur.....and then there is the usual wear-an-tear Tapes do get
and lose their readback strength over time and usage.......etc, etc, blah, blah
Dan