[Amps] peak voltage rating for load cap

[Jim Thomson]

Date: Sat, 19 Aug 2017 16:53:36 +0000
From: Manfred Mornhinweg <manfred at ludens.cl>
To: amps at contesting.com
Subject: Re: [Amps] peak voltage rating for load cap

< Specially with solid state, a blown capacitor can blow up a 
<$200 LDMOSFET.

<Manfred

##  Why would a blown capacitor in a LP  filter  take out the
LDMOS device ??   Where is the high swr protection located, before the
mess of bandswitched LP filters... or after the mess of LP filters ?   What
am I missing here ?   The LDMOS or any other device should have adequate,
and fast protection for any scenario.  Can you put the high swr protection on both
sides of the LP filters ?   Is there any other way to protect the LDMOS devices in the
event of a cap failure in the LP filter ?  

## There are a lot of caps out there that are not RF rated.  IE:  like the pair of
6 kv rated disc ceramics that alpha and others  use for a ..plate block cap assy. 

##  same deal with your garden variety .01 uf @ 1 kv disc ceramic.   They are
NOT RF rated.  However, the  2 kv  version of a .01 uf will definitely handle more 
current than the 1 kv version.   And the 2 kv version is not RF rated either. 

##  But stuff like TV doorknobs are also not RF rated for current.... and the 20-30-40
KV rated types  handle less current than the real deal  15 KV rated  HT-57s.... with
both cases being say a 500 pf value. 

##  I suppose you could also go crazy, and use lower value rated caps ..in parallel, to
handle more current, but then the device count goes way up... and so does the $$  spent. 

## My HT-50 / HT-58   1000 pf @  5 kv rated caps I use for padding my air variables on the 160M
tuned input would run warm, with 200 watts  CCS applied.  They are only rated for 1A CCS.    The 500 
pf version of the same  HT-50 / HT-58 is rated for 3A  CCS.   With 2 x 500 pf caps in parallel, the total 
rating of each padder assy is now 6A  CCS... = stone cold. 

##  manfred, could you make hb caps  from  say teflon, sandwiched between cu straps or plates ?   I have seen
that done............ on lower valued cap assys. 

Jim   VE7RF