[ARC5] Rethinking Recapping, Redux

Fri Mar 23 11:09:54 EDT 2018

Hi all 
FYI I have opened flower pot caps by taking a dental pick and scribing around the mica along the can lip 
Eventually you cut through the mica and pulling the innards out the top. YMMV but is an alternative to cutting metal
73 Mike 

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> On Mar 5, 2018, at 2:39 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> We, ll I'm "in between".
> I too would rather not chase one problem after another, but restore the whole thing, then it's done.
> However, there is something about the the under chassis "flower pots" or whatever you want to call them which gives it that antique military electronics look.
> It's kind of unique.
> I take a pipe cutter to the pots, gut the contents, and replace them with ceramic or mylar caps.
> The cans can be soldered back together because they are brass and look pretty good -especially if I use hot air soldering .
> 
> 
> On Monday, March 5, 2018 2:06 PM, jeepp <jeepp at comcast.net> 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 
> 
> 
> 
> 
> 
> 
> 
> Sent from my Verizon 4G LTE smartphone
> 
> 
> 
> 
> 
> 
> -------- 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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