[Hallicrafters]V18#22; Electrolytic Fireworks

Fri Jul 15 10:31:46 EDT 2005

I worked at Centralab back in the 70's and there was a story circulating 
about one of the engineers there who was experimenting in his cubicle 
with a circuit that included a big electrolytic cap.  He was hunched 
over his circuit when he applied power.  The next thing anybody knew 
there was an explosion like a shotgun blast.  Everybody turned to look 
and saw a cloud of confetti fluttering down on the poor guy.  Yup - 
reversed polarity.  I don't know if the story is even true but it does 
make quite a mental image, and it could happen to anybody.

What's that formula, again?

73, Rich

Phil Barnes-Roberts WA6DZS wrote:
> hallicrafters-request at mailman.qth.net wrote:
> 
>> Re: Re: [Hallicrafters] Recapping Hallicrafters
>> From:
>> peter_may at optusnet.com.au
>> Date:
>> Thu, 14 Jul 2005 13:04:56 +1000
>> To:
>> k0ewu at juno.com
>>
>> To:
>> k0ewu at juno.com
>> CC:
>> radiocompass at yahoo.com, cnicolsen at msn.com, Hallicrafters at mailman.qth.net
>>
>>
>> I once had an electrolyte formula for refilling wet type electrolytics.
>> If anyone is interested, I'll look it up.
>> I also struck the occassional 8 ufd perculating electro. The Ducon 
>> brand Australian ones sometimes had a little rubber valve in the lid.
>>
>> Regards
>> Peter
>> =========================
>>
>>> k0ewu at juno.com wrote:
>>>
>>
>> Harken ye back to the day of wet electrolytics, a tall round can,
>> aluminum, the neg.
>> side. The positive was an electrode in a bath of electrolyte, a water
>> solution.
>>
>> I was working in a gamble store repairing radios after school-- high
>> school,
>> The farmer that brought it in said it souded like his coffee pot.
>> Shure did, I turned it on and it played for a bit, started to gurgle and
>> then
>>   pow!!  the lid of the can blew a hole in the top of the cabinet like a
>> 12 gauge shell would, about 2 in diameter.  from that day forth i have
>> always replaced a wet cap with a more modern one.           Before
>> applying power.
>>
>> jack
>>
>>
>> 1
>> On Tue, 12 Jul 2005 12:18:52 -0700 (PDT) Mike Everette
>> <radiocompass at yahoo.com> writes:
>>
>>>
>>> --- "Clayton L. Nicolsen" <cnicolsen at msn.com> wrote:
>>>
>>>
>>>> "One mistake some make is replacing electrolytic
>>>> caps with one of a higher
>>>> voltage, this will accelerate the aging of the cap.
>>>>
>>>
>>> REST ASSURED!  THIS IS PURE BOVINE
>>> BYPRODUCTS!!!!!!!!!!!
>>>
>>> Sounds like something dreamed up by some propellerhead
>>> whizbang, raised on a diet of germanium and silicon
>>> (especially when made into computers)....
>>>
>>> There is NO danger of jeopardizing a cap by using it
>>> at less than rated working voltage.
>>>
>>> On the other hand, if one subjects some capacitors,
>>> especially electrolytics, to ABOVE rated voltage, the
>>> effect can and often does resemble Mount St. Helens. I once saw a 
>>> can-type filter cap in a tube-type mobile
>>> radio explode, and throw its guts 10 feet straight up
>>> to stick on the ceiling of the shop (it was in an old
>>> garage service bay).  It was LOUD, too. 
>>> And that is the absolute truth.
>>>
>>> 73
>>>
>>> Mike
>>> WA4DLF
>>>
> 
> '----O'=o='O----'
> 
> Pass that formula on, if it comes to hand, Peter!  Most electrolytics 
> come with some kind of a pressure relief port, though it may not be 
> obvious at first.
> 
> I have an electrolytic story; it was at N0EFC at MAG-12, on the beach at 
> Chu Lai RVN, in 1970, running phone patches into N0JPJ at Hughes 
> Fullerton CA, just outside the ham bands on MARS frequencies.
> 
> I was in the middle of a string of calls, and the T/R relay inside the 
> Collins 32S-3 gets dirty and needs a strip of teletype tape pulled 
> between the contacts to clean it (that was our fix; the slight oil in 
> the tape, and the yellow paper roughness, helped remove oxidation 
> without being too hard on contacts.)  Rather than open the hot HV/RF 
> final cage and fiddle with it, while callers are waiting and the band 
> conditions are deteriorating, I swap-in the other transmitter, sitting 
> on the other (vacant) operating position.
> 
> Now the S-line transmitters have the power supply in a separate chassis, 
> often inside the phone patch/SWR bridge/speaker console, and connected 
> by a fat cable with an 11-pin "octal-style" socket, and a plug on the 
> transmitter to match.  This one had happened sometime previously to have 
> had its indexing lug, the whole center post, broken off, so in a hurry, 
> I plugged the thing in, plugged in the various RCA phono plugs (yes, 
> including 100W RF-out to the linear!) and flipped the switch to warm up, 
> so I could get back to servicing customers.
> 
> Naturally, Murphy had a hand ready to deal me.  The indexing was _only_ 
> one pin off, which put primary AC on the bias cap, looking for about 
> -100VDC to Gnd.  After a few seconds more of cooking, it hissed, and 
> then BANG! launched itself across the under-chassis, leaving white crud 
> and khaki confetti in its wake, letting out _all_ the magic smoke. 
> Fortunately, it didn't take out anything else in its trip, and much 
> later in the day, after some research, cleanup and replacing the cap, 
> the (astonishingly well-designed) rig was back in business.  Don't know 
> if that plug ever did get changed.  Meanwhile, to get back on the air, I 
> bit the bullet and unscrewed the RF cage and cleaned my other relay - 
> *Sigh*.
> 
> '----O'=o='O----'
> RULES OF THUMB:
> Replace electrolytics with the same or slightly larger capacity (MF's) 
> and the same or a bit higher working voltage (WV) rating; a good rule of 
> thumb is 50-to-100-percent safety factor in voltage.  Much more than 
> that, and the cap never completely forms properly, and never quite 
> reaches its rated capacitance.  If you have to do that, err on the side 
> of a bit larger capacitance (that will still fit physically in the space.)
> 
> Do make sure of polarity; +/- swapped is another good way to watch your 
> gear smoke!  Have fun, keep it safe!
> 
> 73, Phil WA6DZS at ARRL dot net
> A Task without a Due-Date is a Fantasy!
> '----O'=o='O----'
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