About the best simple thing I ever did amps-wise was to put a piece of
card stock behind the Tune and Load caps, and mark representative
settings for each band on it. Since I did that I don't believe I've
thrown an arc once, simply by always tuning to the band mark *before*
applying drive.
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
On 4/19/2014 10:37 AM, Carl wrote:
That is correct Pete.
There are 2 basic reasons for SB-220 (and most all amps) arcing.
1. Open circuit at the relay, wrong band selected, high VSWR, tuner
(many reasons), remote antenna switch, feedline/connectors, and
antenna. A short may also cause it depending upon location.
2. High RF voltage in the tank circuit, usually during tuning. Making
a tuning chart helps. Adding a 10-12pf 500V silver mica or a 1-3KV NPO
disc ceramic between the 40-20M positions right at the switch will
substantially reduce the risk.
Not having a clue how to tune an amp and swinging knobs all over the
place with close to or full drive is the main cause of arcs.
Often capacitor arc damage can be removed if it is the later erector
set construction by progressively sanding with 1000 to 2000 grit
wet-dry paper and finish with a metal polish. End of the plate melt
downs can be progessively filed down and then the sandpaper.
Carl
KM1H
----- Original Message ----- From: "Pete Smith N4ZR"
<n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Saturday, April 19, 2014 5:35 AM
Subject: Re: [Amps] SB220 tune cap
IIRC, from this reflector years ago, all the change did was to move
the location of arcing to the bandswitch
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
On 4/18/2014 8:10 PM, Jim W7RY wrote:
The later version was longer (more plates) and wider plate spacing.
This was an attempt to fix the arcing issues on the SB220.
Which is usually caused by ALC overshoot in the radio or RF being
sent by the exciter before the antenna relay was energized.
There were 2 holes on the chassis. One for the short capacitor, and
one for the long capacitor. The stud that is between the 10 meter
coil and the bracket on the end of the tuning cap is also shorter
(or removed) when the longer cap is used.
No other changes needed with either cap.
73
Jim W7RY
-----Original Message----- From: Paul Kraemer
Sent: Friday, April 18, 2014 12:54 PM
To: amps@contesting.com
Subject: [Amps] SB220 tune cap
Can someone please enlighten me on two different PA tune capacitors
used in
the SB-220?
I have a 220 I am starting to rebuild and seeing initially that
someone had
"messed" with the PA tune cap I picked up a very clean replacement
on ebay.
It was also mentioned that it was the "later" version PA tune cap.
The two look similar except the "newer" one appears better quality
and has
more plates.
Any other differences in the tank circuit to go along with that?
Thanks
Paul K0UYA
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