[Collins] Repair of 75S1 receiver

[Ron Wicker]

Recently my 75S1 receiver  developed a audio problem The audio is somewhat
distorted and when the audio gain is advanced to a normail setting, there is
a whistle or squeal.  The signal is copyable at certain settings.  I have
checked the tubes and all check OK.Before I tear into the receiver, are
there common things that I should look for?  Any help/advise would be
appreciated.
Thanks, Ron,AA5NI......