[ARC5] Rethinking Recapping, Redux

[DSP3]

Didn't finish my thought!!!!  Anyway, trying to say that I'd rather err 
on the side of prevention, rather that cure.  But, what we have here is 
Ford vs. Chevy.  HI!!

Jeep - K3HVG


On 3/5/2018 2:04 PM, jeepp wrote:
> Well, good comments, all.  In my humble experience, I have had it both 
> ways; that is, some radios will work forever, others not..  I am not 
> of the side of the house that likes to have things, below chassis, 
> original.  Thus, I don't have a problem doing re-caps, especially that 
> which I use or depend on.  Nor do I care to chase issues
>
>
>
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>
>
> Sent from my Verizon 4G LTE smartphone
>
>
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>
>
> -------- Original message --------
> From: J Mcvey via ARC5 <arc5 at mailman.qth.net>
> Date: 3/2/18 22:57 (GMT-05:00)
> To: David Stinson <arc5 at ix.netcom.com>, arc5 at mailman.qth.net, 
> 'Milsurplus' <milsurplus at mailman.qth.net>
> Subject: Re: [ARC5] Rethinking Recapping, Redux
>
> Once upon a time I "let the caps be " on an ARC radio that was running 
> well for several hours on a dynmotor.
> Then, suddenly , the radio went silent and the dynamotor slowed down 
> and was obviously straining.
> Turns out that the large 0.2 uf (?) X3 cap filtering the B+ decided to 
> catastrophically fail to a near dead short!
> Good thing I was there when it happened....
>
> The other ones can do what they do , with little harm to anything 
> other than performance, but that .2X3 cap filters raw B+ and LV.
> Bad things can happen.
>
>
> On Friday, March 2, 2018 3:44 PM, David Stinson <arc5 at ix.netcom.com> 
> wrote:
>
>
> Some may remember a post back in December in which
> I suggested a procedure for reviving sets while
> doing the least amount of tampering and damage
> possible.  The three RAX receivers, which were the
> subject of that post, are still running fine
> (knock wood), one full-voltage on the dynamotor,
> two on a DC-DC converter at 90 VDC reduced B+.
> Across the three RAX receivers, I changed three
> capacitors, no resistors and one tube. Since that
> time, I did repair two bad solder joints in the
> low freq receiver at each end of a bypass cap in
> the BFO circuit.
>
> Recently acquired an unmolested BC-454 receiver
> (3-6 MC) and began resuscitation.
> https://photos.app.goo.gl/2Th2rhu9Coc7qUnR2
> https://photos.app.goo.gl/NBrlsOR72iLcWOBh1
>
> After the obligatory De-Ox-it, lube etc., opened
> the connection to Ground for the Screen Dropping
> resistors, connected +120 VDC to the B+ buss with
> no filament voltage.  This should (with no local
> control in the front) leave no path to ground for
> the 120 Volts save capacitor leakage. Current
> draw was over 20 mills- a certain sign of one or
> more very leaky caps.
>
> Going for the obvious first, disconnected the wire
> to the 5 mFd B+ buss filter, which is not needed
> unless you're going to run the radio on the
> dynamotor.  This immediately dropped the current
> draw to a couple of mills.  I boosted the B+ buss
> (still no filament voltage) to 200V and left it
> there for 2 hours.  Current draw was 4 mA- a minor
> amount of leakage.  So the bypasses were either
> "good" or open.  If open, stage oscillations and
> stage gain would tell me.  Next, the 15 mFd Audio
> PA cathode bypass checked "good." Reconnected the
> Screen dropping resistors, powered the filaments
> and put 100V on the B+ buss.
>
> The radio has been playing well for hours now.  B+
> buss current remains stable.  That's all the work
> it took to get the little soldier marching again.
> Of course, those caps are very old.  They may play
> till Judgment Day and they may quit tomorrow- but
> even if they do, no unnecessary tampering was done
> and the "baddies" will tell on themselves.
> https://photos.app.goo.gl/wXUMwlrZM760F6X62
>
> GL OM ES 73 DE Dave AB5S
>
>
>
>
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