[AMPS] go figure/Murata

[Phil Clements]

Fair Radio sells some large doorknobs for $17 each.  The value is 0.001 uF
and the voltage rating is 20KV.  Murata makes these.  On the cap below the
20KV is 105A. Perhaps I am wrong, but my guess is that it means 105 Amps.

That 105A is a current rating is very doubtful as it would be
meaningless unless the frequency at which it was measured
is given. The old transmitting micas had the RF current AND
frequency where it was measured right on the cap! Gone are
the good ole days of no codes and cyphers. I would guess
the units can easily handle 8-10 amps @ 10 meters. If they
don't get hot, you are OK.

HEC measures the temprature rise on their doorknobs when
RF at a given frequency is fed through the unit.  When the
tempature rises 30% above ambient; that is the current rating
for THAT frequency. They take measurements at 1, 10, and 30
mhz for all of their doorknob line. They allow operation at a 50%
temprature rise with no ill effects, so their is a built-in  fudge
factor for we that push the limit on their products!

I  bought a bag full of those white Murata caps years ago
that were rated at 4900 pf @ 30 kv. I have used them with
several 3CX3000A7 amps with no failures over the years.
I have no idea why the guy on this thread had the failure at
15 meters because he did not specify what tube(s) and power
he was running at the time. I firmly believe these caps are mica,
but I cannot bear to bust one open just to see. Perhaps the
guy with the failed one could look inside his and report to us.

Yes, W8JI, the 4900 pf is way too much but the price for the
bag was  a bargain.

BTW, the threads on the Muratas are metric! Do not try to
force  1/4X20 bolts into them!

(((73)))
Phil, K5PC


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm