[AMRadio] Capacitors


D. Chester k4kyv at charter.net
Sat Dec 30 12:57:40 EST 2006


>> What type of capacitors I should use to replace the paper Astron and 
>> West-Cap capacitors in the rf strip on the sp-600?  I have a good stock 
>> of new Sprague Orange Drops or I can use ceramic disk.  I don't want to 
>> have to do this again.  Of course, at my age, it's doubtful that will 
>> happen!

I tend to use orange drops to replace old wax tubular paper caps, and silver 
micas to replace mica caps.  Disc ceramics have always worked for me to 
replace paper caps, but I prefer orange drops.  I use disc ceramics to 
replace original disc ceramics, but never to permanently replace micas. From 
my experience, disc ceramics are the most failure-prone of all.  The little 
red micas in older Collins gear tend to go leaky over time.  I couldn't 
count the number of these I have replaced in my two 75A-4's and ones I have 
repaired for other people.

One problem I have run into is that many of the standard values of micas and 
silver micas are getting hard to find.  Like everything else offered on the 
commercial market, the variety of choice is steadily dwindling.  For 
example, a couple of years ago I needed a 120 pf mica, or some specific 
value near that (I may not have remembered these figures correctly - and my 
computer is not out in the shack, but you should get the idea).  I could 
find a 100 pf and a 110pf, or a 140 pf, but the exact value was no longer 
listed in any of the catalogues, and the local electronics store said they 
couldn't order that value for me.  Someone sent me a couple of the values I 
needed, that they had on  hand.  They said they had got them from Mouser 
Electronics.

When repairing a piece of antique gear that I want to look authentic and 
original, I gut the old wax paper caps, and refill them with orange drops, 
and re-pour melted wax to seal the modern component inside.  I usually keep 
the original wire leads whenever  possible, since modern caps tend to have 
smaller gauge wire leads  than the older caps.  I never throw away old wax 
caps, but keep them on hand in a special box just for that purpose in case I 
need them.  I have done the same with large rectangular paper and 
electrolytics.

But for something like the 75A-4, I just drop in new components to replace 
failed ones.

Don k4kyv





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