75S1 Purchase

[Glenn Finerman]

I'm posting Bob W5TX's comments (with his permission) because of the
many requests I received for information on the subject of re-capping
older receivers. I hope you find this as informative as I have;
By the way, I did purchase the 75S-1 last night. Turned out to be in very
nice shape with a factory installed CW filter!. All the caps WERE NOT
replaced, just the power supply electrolytics and paper caps. All the
Ceramic and silver mica's were left alone (WHEW!) and the seller did
a real nice job (after a careful internal inspection BEFORE handing over
the money)

Bob said;
re>
In my honest opinion, changing out all the caps is foolish for the
following reasons:
1) In most cases, the caps are still fine and simply don't need changing
out.  There are a few instances of generic problems -- but in the s-line
they are few and far between.

2.) The normal result of such changeouts is a messed up unit. Removal is
not easy in many cases and the odds are that more damage will be done
in the changeout than would ever occur if cap failed!
A few of the generics that I have found are the silver micas in the A
line (small rectangular red caps -- not the maroon dipped units)which
have a penchant to get leaky due to growing of dendrite spurs.  This
apparently is caused by the inability to achieve/maintain a good
moisture seal vs time.  AGC funnies are almost a sure clue as to the
presence of positive voltage on grids of IF stages in A-Line requiring
cap replacement (not wholesale however).  Another is the low voltage
electrolytic bypass on the first audio stage in the S-line receivers.
This bypass may just not have enough voltage across it to keep it
healthy.  Sometimes just shorting across it or any kind of transient
will bring it back to life (temporarily at least).  Occasionally the
"black beauties" in the A-line give problems but for me at least they
are not in the top 10 bad guys.
These are my experiences and others may have other views of course.
Once in a while someone calls and asks what I want to change all of
caps out and I simply say "Don't do it and I won't do it".  A waste of
someones money and my time!
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