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Re: [Amps] SB-220 Plate Tuning Capacitor

Subject: Re: [Amps] SB-220 Plate Tuning Capacitor
From: R L Measures <>
Date: Wed, 7 Jun 2006 04:23:15 -0700
List-post: <>
On Jun 7, 2006, at 3:51 AM, Peter Chadwick wrote:

> Rich said:
> >The measured breakdown potential of a SB-220 bandswitch is c. 4900v
> at sea-level.  At 390v peak output into 50-ohms, the actual potential
> across open bandswitch contacts is c. 2600v-pk.<
> And what is the manufacturer's rating?

Much less, but its RMS.
> For some reason I don't understand, things seem to break down more  
> readily with RF than with DC.
Me neither, but they do, and the effect becomes more pronounced as  
freq. increases.  For example, a Jennings 15kVdc/60Hz-rated vacuum  
cap is rated at 9kV at 30MHz.  I once  built a 4cx250R 70cm amplifier  
that produced c. 1100Vrms at the anode, and the purplish arcs that  
one could draw off the halfwave anode line with a graphite pencil  
were humoungously astounding.   (yes, I was standing on a wood floor  
--  or I wouldn't be standing here)
    As I see it, VHF is more likely to cause arcing than HF or MF.
> 73
> Peter G3RZP

R L MEASURES, AG6K. 805-386-3734

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