[Milsurplus] [ARC5] Rethinking Recapping, Redux

Sat Mar 24 08:37:46 EDT 2018

Hi

Yes, you got it correctly. The 3 mg / 8 hrs is a workplace exposure limit for long term (like years). The
studies aren’t based a lifetime, but more like 5 years. There’s a lot more data to work with that way …
The next layer of confusion comes in when you try to work out how they go from 5 years to “lifetime”. 
There are a lot of assumptions made along the way …..

Bob

> On Mar 23, 2018, at 11:08 PM, hwhall at compuserve.com wrote:
> 
> Mica, per se, isn't dangerous - it's quite chemically stable & hard to get to react with anything.  The issue is inhaling dust.  Cutting a mica sheet out of a flowerpot cap will likely make a tiny amount of inhalable dust but most of it will be tiny flakes not easily airborne.  A whole mica sheet in flowerpot is on the order of a gram or two for perspective.
> 
> Interesting was the explanation of Recommended Exposure Limits as "a level that NIOSH believes would be protective of worker safety and health over a working lifetime."  Does that mean, for example, that the "3 mg in an 8 hour day" is for continuous daily exposures or is it applicable to the sort of infrequent, limited duration represented by tinkering with those radio parts?  Does anyone know?
> 
> Wayne
> WB4OGM
> 
> -----Original Message-----
> From: AKLDGUY . <neilb0627 at gmail.com>
> To: milsurplus <milsurplus at mailman.qth.net>
> Sent: Fri, Mar 23, 2018 5:34 pm
> Subject: Re: [Milsurplus] [ARC5] Rethinking Recapping, Redux
> 
> Caution: Flower pot caps contain mica, and mica is not a benign substance. This article gives figures for tolerable and immediate threat to life concentrations:
> 
> https://en.wikipedia.org/wiki/Mica <https://en.wikipedia.org/wiki/Mica>
> 
> Scroll down to "Health impact" and "United States". I understand the 1,500 mg per cubic meter to apply in a confined space of 1 cubic meter. It's impossible to achieve this concentration with the small quantity in the Command sets. More realistically, the tolerable level of 3 mg in an 8 hour day might be approached, so you'd be well advised to ensure adequate circulating air.
> 
> Neil ZL1ANM
> 
> 
> On Saturday, March 24, 2018, Michael Kana via ARC5 <arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>> wrote:
> 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 
> 
> Warning!  This is transmitted over a non secure medium
> 
> On Mar 5, 2018, at 2:39 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net <mailto: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 <mailto: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 <mailto:arc5 at mailman.qth.net>> 
> Date: 3/2/18 22:57 (GMT-05:00) 
> To: David Stinson <arc5 at ix.netcom.com <mailto:arc5 at ix.netcom.com>>, arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>, 'Milsurplus' <milsurplus at mailman.qth.net <mailto: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 <mailto: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/2Th2rhu9Coc7qUnR2>
> https://photos.app.goo.gl/NBrlsOR72iLcWOBh1 <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 <https://photos.app.goo.gl/wXUMwlrZM760F6X62>
> 
> GL OM ES 73 DE Dave AB5S
> 
> 
> 
> 
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