{Collins} 75S-3B Receiver.



hi group,
Don;t know if anyone is interested in this but it is the continuing saga of
my 75S-3B rx.
I now know that the S5 switch that is fitted is not original (still looking
for one)
Second the Hum issue as I have found it.
On checking it out the HT had a ferocious hum
Using a scope I saw that it was saround 85 volts p-p. yes 85 volts.
Put a few external capacitorsa across C59 sand the hum dropped
considerably. but it was still rough.
Got my LCR meter out and measured the capacitance of C59.
 It measeured  NOTHING, no capacitance value and no ESR on ALL 3 sections..
Checked withanother =3B this morning and all measured as shoukld with an
ESR of about 2.5 ohms.
So it appears that C59 is open, on the negative side , only thing I can
conclude..
One 75S=3b Is now a work in progress till I get a replacement C59.
Don't know if this is of interest but I find it unusual that the Negative
side of a 3 section appears to be open.
Thanks to all who replied to my previous posts on this Rx.
73's
Jim
Ei2BB
CCA -09-12379.



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