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
r@somis.org
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