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[AMPS] Switches and padding caps

To: <amps@contesting.com>
Subject: [AMPS] Switches and padding caps
From: w8jitom@postoffice.worldnet.att.net (w8jitom@postoffice.worldnet.att.net)
Date: Tue, 29 Apr 1997 11:34:43 +0000
Hi Carl,

There may be some confusion about the names of switch 
configurations. There is the slang we use and the names the switch 
manufacturers use.

Switch contacts are manufactured in two basic types, shorting and 
non-shorting. Of the two types, NON-shorting (also called a break 
before make) switches have the highest breakdown voltage.  That's 
because the moving contact does NOT bridge the gap to the new 
stationary contact as the rotor is turned. The moving contact 
has less overlap and more air gap to the adjacent contact. 

A shorting switch makes the new contact before it breaks or 
releases the old contact (also called a make-before-break). This 
requires the contact to have extra metal bridging the gao as the 
switch is in mid position. Because of the contact overlap, 
contact to contact voltage rating is lower.

The correct name for a switch that shorts all previous connections is 
a "pick-up and hold" arrangement.  RSC corp makes pick-up and hold 
switches, the ARD amplifier used this style of contact.

I had a difficult time getting Denny Had to use non-shorting JV 
series switches. He insisted a shorting switch would handle more 
voltage, because he confused the two types. More contact spacing 
(and the addition of arc barriers) ALWAYS translates to more voltage 
in a given switch style. If you look at a NON-shorting JV series 
switch you'll see it has both arc barriers and less contact overlap.

As for the padding caps, most vendors (like ATC) can supply large 
NPO high voltage chips. They have lower ESR and perfect stability 
when used as padding caps. 

Another source are common mica cap suppliers, they offer 
an off the shelf cap called a "snubber mica". Snubber micas are a 
high current low drift 1000 volt silver mica designed for switching 
supplies. Snubber mica's work quite well for modest PA power levels, 
where peak voltages are below 1000 volts peak (say 500 volts RMS  
into 50 ohms, or 5 kW level pi-networks).

Check RF amplifier manufacturers for parts, you may find what you 
need cheaper than through surplus sources.

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