Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: One of Murphy's Laws  (Read 1190 times)
KI4VEO
Member

Posts: 228




Ignore
« on: April 02, 2019, 09:40:37 PM »

A tube will self destruct to protect the fuse in the circuit.  Not logical, but often true
Logged
K7KBN
Member

Posts: 3693




Ignore
« Reply #1 on: April 02, 2019, 10:02:27 PM »

A vacuum tube dropped from a height of six feet onto a concrete floor was good.
Logged

73
Pat K7KBN
CWO4 USNR Ret.
G3RZP
Member

Posts: 1319




Ignore
« Reply #2 on: April 03, 2019, 02:02:35 AM »

An unknown power transformer connected to a 230 volt supply has a 115 volt primary....
Logged
PU2OZT
Member

Posts: 116




Ignore
« Reply #3 on: April 03, 2019, 07:08:57 AM »

After you've cut something (anything) the piece you intended to insert for finishing your long awaited project is always too short and the other end is even shorter. Whatever the junk box your nearby preferred store offers, nothing will fit and you're poised to buy ten times what was initially needed. Obviously it was a project of its kind and the remaining stuff will end up useless for decades.

Oliver
Logged
KC8KTN
Member

Posts: 1929


WWW

Ignore
« Reply #4 on: April 03, 2019, 08:04:26 AM »

When the Wife says I thought you said you would only be on the radio for an hour.. Or are you running that amplifier again..Or is all those antennas on your truck for cb radios..Nuff said ... Keeping it real... 73ss
Logged
NO2A
Member

Posts: 1400




Ignore
« Reply #5 on: April 03, 2019, 10:35:08 AM »

After you spend an afternoon recapping all the Electrolytic capacitors in your beautiful old Zenith, the 2N35 driver transistor will fail. And unless you can find an exact replacement, (that also works) your entire radio is obsolete.     Cry
Logged
N0MKC
Member

Posts: 4




Ignore
« Reply #6 on: April 03, 2019, 01:41:50 PM »

Power supply schematics for tube rigs will have the polarity of one (or more) of the filter capacitors reversed. 

(This will become quite apparent within 90 seconds of commencing the initial smoke test.)
Logged
KD0REQ
Member

Posts: 2404




Ignore
« Reply #7 on: April 03, 2019, 02:28:58 PM »

as surely as every box of nails you buy has half of them with the heads on the wrong end as you grab them, all your new fuses will be defective, and blow as fast as the one that was in the rig for 10 years. guaranteed. trust me on this.
Logged
KX4QP
Member

Posts: 404




Ignore
« Reply #8 on: April 03, 2019, 03:38:12 PM »

A tube will self destruct to protect the fuse in the circuit.  Not logical, but often true

I first read this forty-plus years ago, in the form "A 49 cent transistor will save a two cent fuse by blowing first."  It was old in the 1970s, of course...
Logged
W9FIB
Member

Posts: 2530




Ignore
« Reply #9 on: April 04, 2019, 01:10:15 AM »

Each electronic device is made with a certain amount of smoke built into it. Once you let the smoke out, it does not work anymore.
Logged

73, Stan
Wisdom is knowledge you gain after you know it all.
SWMAN
Member

Posts: 1349




Ignore
« Reply #10 on: April 04, 2019, 03:51:19 AM »

FIB you are correct but, Radio Shack once sold that smoke in a can so you could extend the life of your devices for much longer. I stocked up on it when they went out of business, still got a few cans laying around. I'm not really sure if you can still buy it anywhere else or not.
Logged
G3RZP
Member

Posts: 1319




Ignore
« Reply #11 on: April 04, 2019, 01:59:34 PM »

Once, many, many years ago, a number of Plessey Semiconductors (note Plessey Semiconductors were bought and changed name in about 1987 so it was a very LONG time ago!) some military grade IC s came back for leaking water!. They had been submerged for the fine leak test, but the welds were so defective on the cans that they had a gross leak which wasn't bad enough to appear when devices were handled, but which only appeared when the customer put them in equipment and electrolysis increased gas pressure in the can...

No smoke there! But a hell of a lot of red faces in assembly, test and QA!
Logged
KC6RWI
Member

Posts: 211




Ignore
« Reply #12 on: April 04, 2019, 02:14:16 PM »

I don't have the exact phrase for this one figured out, but sometimes in trouble shooting we go for longer involved repair instead of checking for the simple first.
Logged
KX4QP
Member

Posts: 404




Ignore
« Reply #13 on: April 04, 2019, 03:27:56 PM »

I don't have the exact phrase for this one figured out, but sometimes in trouble shooting we go for longer involved repair instead of checking for the simple first.

Where I work (fixing power tools) we have a saying -- "fix the cheap stuff first."  That is, never start by replacing the most expensive part in the tool; start with cheap bits (brushes, cord) and see if that changes anything.
Logged
K7MEM
Member

Posts: 723


WWW

Ignore
« Reply #14 on: April 04, 2019, 03:48:23 PM »

Power supply schematics for tube rigs will have the polarity of one (or more) of the filter capacitors reversed. 

(This will become quite apparent within 90 seconds of commencing the initial smoke test.)

[true story]
When I was in high school, (1965-1967) our electronics shop had open framed televisions to work on. (Child safety was not a big issue back then.) One day the electronics instructor was working on one of the televisions and replaced a high voltage electrolytic. You know the kind, tall aluminum cans rated at 350 volts or more. While leaning over the television chassis, he turned it on. Within about 10 seconds the electrolytic blew up. The aluminum can shot right over the instructors shoulder, narrowly missing his head. The shell traveled about 40 feet, with a trail of tin foil and paper confetti. No smoke, just a red face on the instructor.
[/true story]

I don't have the exact phrase for this one figured out, but sometimes in trouble shooting we go for longer involved repair instead of checking for the simple first.

Where I work (fixing power tools) we have a saying -- "fix the cheap stuff first."  That is, never start by replacing the most expensive part in the tool; start with cheap bits (brushes, cord) and see if that changes anything.

[another true story]
When I was a technician, working on the bench, one of the other technicians had an nice small electric drill. It was incredibly handy. The technician wanted to use it to drive 2-56 screws into our circuit boards. We usually did that by hand, because the screws only needed to go in a short distance. But the small drill wouldn't stop immediately, when you released the trigger. So it would always drive the screws too far. Sometimes, far enough to strip the threads in the board. So one day, he had the brilliant idea to wire a couple of diodes across the switch so that, when the switch was released, the diodes would short out the motor and stop it immediately. What he didn't account for, while the drill handle exploded in his hand, was the reverse EMF from the motor. The drill wan't very handy any more.
[/another true story]
Logged

Martin - K7MEM
http://www.k7mem.com
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!