AF6AY wrote:
On Mar 23, 3:32�pm, Joerg
wrote:
AF6AY wrote:
On Mar 21, 4:31 pm, Joerg
wrote:
AF6AY wrote:
"Joerg" posted on Fri, Mar 20 2009 6:06 pm
ken scharf wrote:
JIMMIE wrote:
Relays are ok in those applications, where there are actual currents
flowing. What I meant was pure signal switching with no DC currents.
That's called "dry" switching in the electronics industry, has been
called that for over a half century.
Sealed relays, Reeds, mercury-wetted and such work quite well there. But
non-sealed versions have issues and a snap-on plastic cap ain't a seal.
Didn't say that that it was a seal. �But...there are many kinds of
'seals' and there are many kinds of contact alloys which few hobbyists
investigate.
Most must make do with whatever places such as Digikey offer at
affordable cost.

I disagree considering that Digikey is one of the largest
distributors
in the world of electronics and offers so many different models AND
price ranges. Then there is Mouser, and Newark, and Allied, and
Jameco, and Ocean State, and Futurlec, and....a whole bunch of
them. None of those are 'giving away' anything.


Sorry, maybe I didn't express it well enough. My point was that not
everyone has a mil budget or a Rockefeller-sized bank account ;-)


Sure, but in a car relays always switch something that draws a serious
current, more than a few milliamps. That works for a long time. Well,
until a "weld wart" shows up, like it did on a relay in out Genie garage
door opener.

I will disagree again, but not on our particular Chevrolet...I only
got a
glance at the electronics wiring manual at a local dealership service
shop and NOT all the controlled circuits were "serious current" ones.
But, if you are convinced that they ALL are, I can't convince you...


Interesting, my car doesn't have that. Now I am curious. What are they
switching in a car where there is no DC current?


Hmm, I've had that happen even in $xxxxx lab gear, not quite
consumer-grade. Never really with mil gear though but those guys can
often design to "the sky's the limit" cost goals.

Sorry, but that is URBAN MYTH among amateurs. What amateurs
don't realize is that components are elevated in cost by EXTREME
ENVIRONMENTS required. Sure, everything at room temperature
works dandy and one can use any kind of schlock parts and get away
with it. Freeze it below brass-monkey temps or heat it more than
boiling water, drop-kick it across the room, run it under extreme
vibration, it MUST WORK. Put most ham gear through that and you
won't have enough left to sell anything but its manuals on e-bay.
Been
there, done that for years...its what I did for a living.


As I said this was high-Dollar lab gear. The kind where they don't even
flinch when an engineer says "this needs a piece of rigid coax".


----------------on the AN/PRC-104 HF transceiver
But I bet no expense was spared to pick the very best parts for that radio.

I'll bet you've never seen the inside of it, let alone talk with any
of the
staff at Hughes Ground Systems that designed it. If you want to
investigate it, the TMs (user to depot level) are available on the
'Web.


I've served (army), had to deal with radio/telco equipment. Cleaned many
relays there with Emery paper and alcohol. There is a reason for
instructions like this:

http://www.ansaldo-sts.com/EN/Ansald...y_Cleaning.pdf


Hard to find and you may need special clearance to access some
military sites nowadays, but it is available for nothing. If you want
to
pay money for such a manual, fine, those are easier to get.

Sealed relays are ok.

Thank you for such permission. I was using salvaged components
from junkyard electronics a half-century old and know how to test
things that are salvaged. Note: I'm not just making conversation
here,
I'm trying to point out a few things which defy Urban Myth and what
the ARRL deems 'useful' for amateurs.

I also have a few really old ones here and so far
they have never let me down. But I don't have enough to equip a filter
bank with 15-20 in- and outputs. For that I've got a stash of HSMP-3810
PIN diodes.

I'm not swayed or impressed by a bunch of house numbers. Neither do
I need over a dozen different things switching in/out. For that
matter, I've
tried out 3-penny-apiece 1N4148 diodes (100-lot price), plain old
ordinary
old-fashioned silicon switching diodes and they could work just fine
for
4 different HF circuits...but NOT easily for B+ at 100 VDC...and they
need
more circuitry for controlling them than just relay coils needing only
a back-
EMF clamp diode.


Yep, usually a resistor plus on occasion a choke in series with it, and
enough voltage to be able to be able to reverse the diodes far enough.


But, what the hey, if you are convinced in only your way of doing
things,
fine, go do it. Excuse me, I'm going off-line and spend some quality
workshop time putting some hardware together. QRT.


Have fun :-)

I am going to have to repair a bench supply that blew its power
transistors way down in there. Not much fun.

--
73, Joerg