[Amps] Russian capacitor kbap ratings to current?

[Jim Thomson]

Date: Fri, 4 May 2018 11:42:20 -0400
From: Peter Bertini <radioconnection at gmail.com>
To: amps at contesting.com
Subject: [Amps] Russian capacitor kbap ratings to current?


<I have several 470pF @ 15kV RF doorknob caps that have a 40kbap rating.
<Seller says the kbap markings are the same as our kvar.

<How do I calculate the maximum RF current these can handle?

<Is this the correct formula? (assuming they are well within their frequency
rating.)

*I = kvar x 1000 / Vrms x 1.73   *

73

Pete

##  You cant.   I just went through this exact same thing last week  with  
russian doorknob caps. 

##  The best I could come up with is to go to HECs  site, high energy corp in the usa,
and compare their graphs for similar rated doorknob caps,  similar vdc, similar pf ratings,
and similar kvar ratings. 

##  EG,  the  HEC  HT-57 series.... or centralab version.  BTW, centralab is now  ITT / jennings.
HT-57 series is  15 kv rated, and  35 kvar.   BUT the current  rating depends on freq used, and also
cap  value.   KVAR is a bit of a misnomer.  IF say you want it for plate block cap use,  you have to 1st
calculate the current through the  block cap.    And plate block cap current will be equal to the  current
that flows from anode to grid on a  GG Triode.   Take  key down  B+  voltage  and multiply by .6
Take that result and   divide by the XC  of the anode to grid C.    You have to know what the anode to grid C
is... WITH the tube plugged into socket.   Which is always  higher  than when its on the wooden bench.
XC  of course will vary with freq in use.  Lower freqs will have higher XC... and higher freqs  will have lower XC. 

##  Next  calculate the XC  of the plate block cap  on a specific freq, like both  160m and also 10m.  Once u  have calculated  the current through the block cap,
then multiply the  block cap current  by the calculated  XC  of the  block cap.   That result will give u the RF  RMS V drop across the block cap.   
Then its easy to calculate the KVAR  through the cap.    block cap current squared  times XC.    Or   RF  rms V  squared..... divided by  XC.  

## The voltage across the cap is typ not very much.  BUT, it is in addition to the B+ across the block cap. 

##  IF on the other hand its  going to be used for padding a load cap etc, then  just calculate the XC of the cap on a specific freq.  Then calculate 
the  rms  RF voltage across the cap.  Current through the cap will be    V  divided by  XC.  

##   U need to go to HECs  site... and find a comparable  looking cap to the russian one.  If it’s a puck style, HEC also has those listed. 
Don’t assume anything.   U will see at a glance, that  depending on cap value, the rated current will vary greatly.   EG, the highest current rated cap
in the HEC   HT-57 series is the 200 pf cap...rated for 15 A.   Go above or below this value... and  current ratings drop off. 

##  Typ  generally speaking, on the lower freqs, the current rating drops off..and  max V  across the cap  increases.  On higher freqs, the current rating
increases..and   V rating drops off.   HEC  will depict on their graphs for each cap,   a graph of freq  vs  current, voltage and also KVAR. 
http://highenergycorp.thomasnet-navigator.com/category/ceramic-capacitors

##  HEC  will stamp the series, like HT-57  on their caps, and also  XXX  pf and also 15 kv,  but nothing else.  No current rating  and no  kvar rating.  

Later... JIm   VE7RF.