[Amps] SB220 tune cap

[Pete Smith N4ZR]

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 at contesting.com>
> To: <amps at 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 at 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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>>
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>
>