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Re: [Amps] RF Power Capacitors

To: <>, " AMPS" <>
Subject: Re: [Amps] RF Power Capacitors
From: R.Measures <>
Date: Mon, 12 Jan 2004 07:23:45 -0800
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** Hal --   A source of RF transmitting capacitors is:
  However, 2000pF is not needed for a pair of 8877s' DC blocker capacitor 
unless the anplifier is for AM broadcast-band service.  My guess is that 
700pF would suffice for 1.8MHz.  Thus an HT-59, 700pF, 25kV-DC unit, 
which will carry 14A at 10Mhz should do the job.   However, HT-59 Series 
caps over 250pF should only be used by coupling and bypassing since they 
have N3300 or N4700  temp coefficients.  //  note --- I would avoid 
paralleling DC blocker caps since doing so forms an additional 
VHF-resonant circuit in the anode-lead which can be a pain in the 
--   It is my opinion that Hams typically choose DC blocking caps that 
have needlessly low Xc for what is basically a high-Z circuit -- i.e., 
they use more C than is justified..  Afterall, the DC blocker cap 
dissipates virtually no power no matter what value it is.  The main 
criteria is whether the Tune and Load capacitors will tune the tank for 
max P without touching their stops on the lowest freq. of operation.  If 
they do, the DC blocker has enough C.   //  A couple of years ago Tom 
Rauch, W8JI, reported on a fellow who mistakenly used a 100pF instead of 
a 1000pF DC blocker cap. in a 1500W HF amplifier project.  The amplifier 
worked as expected.  However, when the mistake was inadvertently 
discovered, the 100pF unit was replaced with.a 1000pF unit .  No change 
in power output was observed.  

>Would somebody recommend a source of transmitting RF Power capacitors
>that would handle 5 or 6KV, provide about 2000pF, carry 11 amps and be 
>suitable plate blockers for 2 8877's, please?
>There are a couple of ebay items at 10KV, but I don't know if
>they are rated as plate blockers. 
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