{Collins} Re: Replacing Capacitors



David,
My experience has been very good with JustRadios electrolytics too- they work just fine in Collins and other tube-type receivers. In restoring old sets I usually leave the above-chassis-mounted cans in place and add small single-section replacements underneath. As with the metallized foil caps, I always try to use ratings well above the working voltage. Will they last as long as Sprague caps? It's not possible to know, I think, but all modern caps are built with much better precision and technology than the originals were, so I imagine both Sprague and most others will last longer than you or I will need to worry about it, assuming they are used within their ratings. One exception- there have been some recent problems with Chinese counterfeit Nichicon and other name brand capacitors- those can't be trusted! However, I've only heard of counterfeits in SMT types: maybe someone else on the list knows if there are counterfeit leaded types around....

With a good cap checker in good condition you can apply voltage in increments to an electrolytic cap-up to its rated voltage (and a bit over) and watch the dielectric re-form by the opening of the shaded segment in the "magic eye" tube. In new caps it's usually within a second or two: with older caps it can be many minutes at slowly increasing voltages. I like being able to actually "see" an electrolytic cap re-forming in this way. If the dielectric is beginning to break down the segment flickers, and if the segment doesn't open very far, then the dielectric is leaky. Once an older cap's dielectric has fully re-formed it will usually stay properly formed for a long time. If it doesn't, replace the cap!

By the way, many of the older cap checkers (like my Heathkit IM-18) are old enough so you need to re-cap them! Be sure to use accurate caps in their bridge circuits. Also, check the resistors in the high voltage circuit: they seem particularly prone to changing values. Amazingly, I've found quite a few electrolytics from the 1940s and 1950s that re-form just fine, but if I leave such oldies in the circuit I always put an appropriate in-line fuse in the AC line under the chassis. If it's at all convenient I replace all electrolytics >40 years old for reliability.

Hope this is useful to you.
Cheers,
Fred VE1FA


At 10:52 AM 03/05/2008, you wrote:
Fred,

What is your opinion on the electrolytic capacitors sold by Just Radios.  I
have always bought Sprague Atoms for replacement electrolytics from Mouser
when I needed them.  Just Radio's prices for electrolytics is 1/2 or less
than the Atoms price.  The local electronics supply store sells the same
capacitor but I have always stayed away from them.  Comparable capacitors
about 2/3 the size of Atoms.  I have equated the with lesser quality.

Is there a difference in quality/life/performance that would justify paying
the higher price?

David
KC2JD/4

> -----Original Message-----
> From: Fred & Helen Archibald [mailto:hfarchibald@xxxxxxxxxxxxxxx]
> Sent: Friday, May 02, 2008 6:32 PM
> To: dhallam@xxxxxxxxxxxx
> Cc: collins.mailman.listserve.com
> Subject: Re: {Collins} Replacing Capacitors
>
>
>
> Hi David,
> I've used hundreds of new metallized film caps in re-capping and
> repairing all kinds of 1930s-1960s Collins and many other tube
> receivers. So far, I've had 0 cap failures or problems due to these
> caps. I always use caps with voltage ratings well over the working
> voltage of the circuit: in fact I buy only 400 and 630V rated caps
> for most values less than 0.22uF. Transmitting caps handling
> significant RF current would be another story!
> I also check each on a good old HV leakage-detecting type cap tester
> (a re-capped Heathkit IM-18),  before installing it. They always
> have > 100 M ohms DC resistance at their rated voltage. By the way, I
> find cap prices and service excellent at JustRadios (on-line). No, I
> have no association with them!
> Hope this is useful to you!
> 73
> Fred VE1FA
>
> At 05:59 PM 02/05/2008, you wrote:
> >When replacing paper capacitors in our radios, what are the opinions of
> >metallized film vs. film and foil.  Looking at the various manufacturers'
> >websites, I don't find any definitive answer to choose one over
> the other.
> >Metallized film capacitors certainly less expensive but is price really
> >equated with performance.
> >
> >David
> >KC2JD/4
> >
> >
> >.
> >SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
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SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
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NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
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      1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)




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