[Milsurplus] Re: [Hammarlund] Oil-Filled Caps (BC-779)

[Al Parker]

Hi Joe,
    I meant to get back to you after your post on your "final report" on
the BC-779, but somehow things got away.  May I use that info as an
addition to my webpage?  It should be of help to follks.  Will give you
credit, of course.
    On the oil-filled caps, as long as they're not leaking, they should
last 'forever'.  You can do a very rough ck with an ohmeter, the meter
will go immediately toward zero ohms, then should build up fairly quickly
to over a megohm, and keep on going.  That'll show it's got capacitance,
only doing a comparison to a known value will give you a rough
quantitative measure of how much.  An ESR meter is the best to determine
the quality of a capacitor (Equivalent Series Resistance).  There is some
way to simulate it, but I don't remember just what.  I think the EXR mtr
uses a pulse at 1kc or more, and reads out in ohms, from milli-ohms to 10
or above, the lower the better.  Or do as was suggested, just measure the
ripple you get.
    600v is a bit over an overkill, but probably an easily reached  no.
for oil filleds.  If you replace with electrolytics, use something at
least 10% over the actual voltage.  450v for the HV, lower for the others,
but if one of the bleeder/divider resistors fails, you might get full HV
on the LV section, I don't remember exactly the setup.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.boatanchors.org
http://www.hammarlund.info

----- Original Message ----- 
From: "Carole White-Connor" <carolew at bellatlantic.net>
Cc: <hammarlund at mailman.qth.net>; <milsurplus at mailman.qth.net>
Sent: Saturday, January 20, 2007 10:34 AM
Subject: [Hammarlund] Oil-Filled Caps (BC-779)


>     I'm working on a power supply for a BC-779. It has the original
> oil-filled filter caps. I have yet to fire it up. However, I intend to
> use this BC-779 and power supply on a regular basis for SWLing. The
> receiver is a great-performing set.
>
>     Here are my questions:
>
>     1. I understand that these oil-filled caps are more reliable than
> electrolytics of the same vintage. However, what is the consensus on
> whether they should routintely be replaced?
>
>     2. How can I test them? I do not have a cap checker. I will have to
> use a VTVM.
>
>     3. These caps are rated at 600 WVDC. Is that overkill? What would be
> the recommendation for the voltage rating of replacement caps?
>
>     As always, thank you for your help and guidance.
>
>                             Joe Connor
>