[Johnson] Ranger fuses

[John Lawson]

On Sat, 18 Feb 2006, SBJohnston at aol.com wrote:

>
> I've been really surprised by the venom of several messages I've received
> off-list regarding my fusing of my Ranger.  I would never have guessed that I'd
> be called such nasty names over a technical issue like this.  Wow...   Really
> makes me glad to be part of this fine fraternity.


    It seems to be an unfortunate 'artifact' of a lot of "clubby"-type 
hobbies: there's always group of Old Codgers whose 'opinions' are 
sacrosanct and whose grasp of social skills seems pitifully lacking.  I am 
sorry that such person(s) would take the time to write you nastygrams.

   I always chant, and teach, my HamRadioMantra: "It's Only A Hobby; It's 
Only A Hobby; It's Only A Hobby...."

   That being said, I wish to respectfully and humbly offer that I still 
don't think you're getting the Underlying Point in all this.


>
> One follow-up point I'd like to make...  The Ranger, at least the one I own,
> is a balanced AC load.  The AC cord enters the rear and passes immediately
>
   [snip]

> I'm not trying to convince anyone to do it my way - just make my reasoning
> clearer.

    It's not a case of anyone's particular "way".  You are not, I think, 
taking into account the very likely event of a short-to-chassis fault 
inside the Ranger (or Valiant, or %_device) that then places Mains Hot on 
said chassis.

   And your reasoning is quite clear, and electrically logical and correct. 
I would however presume to offer that it's just not at all "safe"

  In fact I have a Ranger on the 'please fix me someday' shelf with just 
this problem, save that it's the 5V rectifier filament windings that are 
smoked and shorted. To the laminations. To Ground...  Then too, in every 
Johnson BA rig I've worked on, there is very elaborate baypassing of all 
lines in/out - coils in series and caps to ground. 50-60 years on, these 
caps, especially the ones that bypass HV and Mod and Mains, get 'tired' 
and begin to fail.

   The folks who designed most of this generally got their training before 
WWII, and certainly used 40s era technology and design concepts in the 
execution of the early transmitters. With the passing of time, we have 
grown a lot more 'mature' in our approach to this, especially safety - 
which, of course, is now a module on the Ham tests....  covering just 
these subjects.



>
> Interesting side note: the six chinese-made IEC ac cords I've so far found
> that had their hot and neutral wires reversed *inside the cord* certainly
> invalidated any distinction between the two on the computers that used them as
> cords.


   There are a series of Large Military Aircraft flying today, for which my 
company supplies rebuilt and remanufactured tooling, test sets, etc. One 
particular test box (for which we have a maintenance/upgrade contract) 
initially came to us with the occasional ground system actually burned 
(sometimes wires would fuse off inside the teflon insulation, but not melt 
- what Fun that was!!) as well as the power supplies showing up just 
french-fried, but with no downstream 'reason' - the PSUs would arrive 
having commited apparent suicide. Nothing we could do would get them to 
fail in a controlled environment, and as well they never smoked in 
calibration in the field - just once in a while in actual use.

   In discussing this with the various maintenance chiefs and crews - it 
suddenly became apparent that the only common factor were the 'convenience 
outlets' in the cockpit of the planes - put there especially for all the 
test boxes, scopes, soldering irons, etc. needed to do maintenace and 
repairs.  The techs would tell me that they often got 'bitten' or that one 
had to be sure to hook up the cables first, then plug the boxes in - or 
that folks ended up wearing gloves when using the test boxes...

   Of course it turned out that not quite half of these outlets (just 
standard white 'wall plug' types, two in each plane, were wired with Hot 
and Neutral reversed.  At least one cockpit fire, and several (thankfully 
non-fatal) injuries, were able to be traced right back to this fault - 
that had existed since the planes were built, some 30 years previously.
A genuine case of "Whodathunkit??"...



   The Point being that some of this safety-related Stuff doesn't seem 
intuitive from a purely 'electrical' standpoint - but when one re-frames 
the concepts in terms of life-safety issues, then they begin to take the 
weight that they desperately need.


    Cheers!

John  KB6SCO