1953 bad year?

[ittam]

Hi! Just wondering if someone could advice me with this strange behaviour
of Behringer 1953 pre I got used. Please no typical B... crap talk just now!
Channel 1 is OK but channel 2 sort of "locks" or heavily overloads if I raise gain either by input gain
or output gain,this happens near max. gain. Works and sounds OK at decent levels
and as said ch. 1 doesn´t do this. Is there a component failing, kind shorting the
channel or... I´ve changed tubes but no influence -originals or new ones -as expected. This does´nt happen when I use the line in so it must have something to do with the mic pre stage. I´ve cross checked my other components in the signal chain and no trouble there.
It would be nice to be able to use max gain with both channels,as I´m
thinking of buying some cheap ribbons, but cannot afford a good preamp at the moment.

Thank´s for any...
Matti