I have 2 geriatric, yet beloved Panasonic 10-transistor solid state
radios - model R-307 (early 1960s vintage), for one of which the
front-end sensitivity on MW (using its internal ferrite-rod antenna)
suddenly dropped to practically zilch after connecting to a 13-meter
long-wire external antenna soon after acquiring it (second-hand).
However, if the external antenna is connected directly to a terminal
adjacent to the on-board MW antenna trimmer, it pretty much gets back
to its normal operating state. I also own the Sangean mentioned in the
subject line above. Having read at
www.jazzkeyboard.com/jill/radio/faq.html#static about a common fault
re the Sangean's front-end transistor Q115 which apparently quite often
blows in the presence of static build-up on the external antenna, (mine
hasn't yet blown-touch wood!) - could the same have happened to the
Panasonic's front-end RF amp - a 2SA70 transistor - from its circuit
diagram? Probably not really worth spending much on this ol' "dunga"
but it would be nice to restore it again....