[Amps] SB-221 parasitic supression upgrade kit

[Carl]

Dirt, especially in already arced cap plates dont get better with use. 
Enough times and it takes out switch contacts.

Find a 10-12pf 1KV silver mica or a 2-5kV ceramic doorknob and wire it 
directly across the 40-20M switch contacts. This will snub the very high 
open circuit RF voltages that cause 99% of SB-220 problems and not 
phantom parasitics.

You may have to spread the 10M coil section a bit to be able to tune.

Carl
KM1H


----- Original Message ----- 
From: "Vic K2VCO" <vic at rakefet.com>
To: "Amps reflector" <amps at contesting.com>
Sent: Thursday, November 20, 2008 4:50 PM
Subject: Re: [Amps] SB-221 parasitic supression upgrade kit


> Rick Stealey wrote:
>>
>> If your amp used to be stable why do you think it would suddenly 
>> start arcing, or go into
>> parasitic osc.?  It IS possible the resistors in the parasitic chokes 
>> changed value, and that
>> should be easy to change if so.  Expect them to have increased in 
>> value but see how much.
>> But you should also look carefully at the bandswitch because that is 
>> a troublesome item
>> in that amp.  Also make sure your output relay is clean.  And look 
>> down in there carefully
>> when it is spitting and see where it is occurring- you might just 
>> need to clean or burnish
>> a plate on one of the variable caps (where it might have arc'd once 
>> when not tuned properly
>> and a little burr developed.)
>> The issue of replacing parasitic chokes with those of a "new" design 
>> has been debated
>> on this list through 1000's of postings.  I happen to be in the camp 
>> that says, "If it used
>> to work, just find out what changed over the years, don't redesign 
>> it."
>
> I would agree with all of the above and add that the arc could be
> occurring in the tube, if it is gassy.
>
> Parasitic oscillations rarely (if ever?) cause arcs anyway, so this is
> probably the least likely scenario.
> -- 
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>