[AMRadio] Suggestions for restoring a DX-100

[john_walker_beasley]

Bill thanks again,

    You guys are like owning a radio encyclopedia !

John ....


----- Original Message -----
From: "Bill Smith" <billsmith at ispwest.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, April 03, 2002 3:53 PM
Subject: Re: [AMRadio] Suggestions for restoring a DX-100


> There are two major considerations, leakage and power factor.  Given
> unlimited wealth, of course the best solution is to use new caps and throw
> the old ones away (or use them as shells to make rebuild caps).
>
> Some (and many by all means are just no good anymore) caps can be brought
> back to service.  George mentions caps he has fought, with poor results,
and
> I have had the same experience.  But I have a lot of old radios that are
> running just beautifully with their original electrolytics, too.
>
> All you can do is try reforming them.  If you have to tease the leakage
out
> of them, they are likely not going to provide good service.  If they have
a
> high power factor (as measured with commonly available capacitor testers),
> they have opened up, and are defective.  Sometimes power factor will
improve
> with reforming, but I wonder at the quality of the cap.
>
> If you can add a diode to a transformer, you have built a simple dc
supply.
> Add a millampere meter, you have a reforming circuit.  Add a good sized
> resistor in series to make the job easier and provide some sort of
> short-circuit protection.
>
> 10 ma/ 350 volts = 35K resistor.   Anything around that value will be ok.
>
> W = E^2 / R, or 350v ^2 / R = 3.5 watts, use a 10 or 20 watt resistor.
>
> Hook the thing to a light-dimmer or a variac.  Keep the reforming current
> under 10 ma and gradually increase the voltage over a period of hours to
the
> rated value of the capacitor.  Some caps may take a day to reform,
> especially if you maintain a low charging current (about 1-2 ma).  After a
> day, set the cap aside for a week or so, then try charging it again.  If
the
> cap shows high leakage, or a high power factor, it is probably spent, but
if
> it acts as a new capacitor you have saved a good part.
>
> 73 de Bill, AB6MT
> billsmith at ispwest.com
>
>
>
>
> ----- Original Message -----
> From: "Todd Bigelow - PS" <tbigelow at pop.state.vt.us>
> To: <amradio at mailman.qth.net>
> Sent: Wednesday, April 03, 2002 12:43 PM
> Subject: Re: [AMRadio] Suggestions for restoring a DX-100
>
>
> > I have a set up made for me by a friend. It consists of a piece of
> something
> > copper-covered (like circuit board, but more flexible)onto which he made
a
> > trace(gap) separating two regions. Then(IIRC), some scroaty diodes
between
> the
> > two areas and a clip lead soldered to each for attaching to a variac. I
> *think*
> > the idea he came up with was to solder the cap leads to the copper
regions
> and
> > run the variac up, while at the same time monitoring with a VOM(leads
> placed one
> > on each region of foil). It's been a few years since I looked at it, so
I
> could
> > be in error here. He used it to reform the new caps in my spare 30L-1(on
> > long-term loan to him) when he replaced them. He then passed the stuff
> onto me
> > and I had every intention of going through my filter caps and renewing
> them,
> > just never found time.
> >
> > Questions: one would guess that reforming would work fine as long as the
> > electrolyte is in good shape, but how can you tell until it goes *POW*?
> Wouldn't
> > it make sense that this stuff has dried out over the years resulting in
an
> > otherwise-new cap becoming shorted? In other words, even if you can
bring
> a cap
> > back to life slowly, how safe is it in your gear?
> >
> > Just curious. I have a bunch of NOS Twist-loks and a number of the 4-pin
> octal
> > base units that I'd love to be able to use, but it almost seems like
> gutting and
> > rebuilding would be better from a safety standpoint?
> >
> > de Todd/'Boomer'  KA1KAQ
> >
> >
> >
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