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Re: [Amps] SB220 tune cap

To: Carl <>, Pete Smith N4ZR <>, "" <>
Subject: Re: [Amps] SB220 tune cap
From: Robert Groh via Amps <>
Reply-to: Robert Groh <>
Date: Sat, 19 Apr 2014 08:32:31 -0700 (PDT)
List-post: <">>
Great info, Carl - thanks.

Bob Groh, WA2CKY

 From: Carl via Amps <>
To: Pete Smith N4ZR <>; 
Sent: Saturday, April 19, 2014 9:37 AM
Subject: Re: [Amps] SB220 tune cap

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.


----- Original Message ----- 
From: "Pete Smith N4ZR" <>
To: <>
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
> blog at
> 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:
>> 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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