[Hallicrafters] SX-28 hum

[Jon Miccolis]

Hello,

I recently rescued from a neighbors shed a pretty decent sx-28, brought it up
nice and slow on a variac, and have been running it "as found" for about a
month.  Up until yesterday evening it was operating without a hitch - clean,
crisp audio, nice and sensitive, and no hum whatsoever (quite a testimony to
how well built the receiver really is).  Well, while listening to AM broadcast
it suddenly went to a loud hum (electric razor like).  The hum persists on all
bands and remains even when the volume and gain are at zero.  Well, almost
needless to say, I immediately suspected capacitors.  Although I intend to
eventually recap, etc.  I currently am without the time and would just like to
correct the problem at hand with minimum time/money expenditure.  My question
is this (and to most it may seem quite elementary):

Does the "hum" problem seem more symptomatic of C51 and C52 A-C line bypass
caps, C48 and C49 input/output filter caps, or both?  And if C48 and C49 what
has been found to be the best (and most cost effective!) replacement option?  

As always thanks in advance for the assistance!

Jon, KB9WVK