[AMPS] SB-220 TUNE Cap Arcing

[Rich Measures]

>
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>> Subject: Re: [AMPS] SB-220 TUNE Cap Arcing
>> Date: Tue, 13 Oct 98 15:35:21 -0000
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>> From: Jon Ogden <jono@enteract.com>
>> To: "Norell  Bennett W." <bnorell@lge.co.kr>
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>> >I haven't had a chance to tune up to see any difference yet.
>> >If arcing still occurs, and if it is possibly parasitics
>> >at 110MHz as Rich comments, what can be done?
>> 
>> If the supressor resistors are OK, then my bet is that they are working 
>> fine and you don't have parasitics.  

However, R-sup is MOF, not carbon composition, so they are much more 
tolerant of overloads.  The Matsushita 3w-rated MOF resistors we use in 
our suppressors will dissipate 12w each in free air for 1hr. with little 
effect.  

>>You already have nichrome wires in there so adding Rich's wouldn't do 
anything for you.
>>
Nichrome (resistance wire) is not a cureall parasitic-oscillation 
vaccination.  When the optimal amount of L-sup is used, the 
improvement/decrease in VHF Q with resistance-wire compared to 
copper-wire is c. 40%.   If not enough L-sup is used, a nichrome-wire 
suppressor could have a higher VHF Q than a copper-wire suppressor with 
more inductance. j.  As a test, squeeze the turns of L-sup closer 
together to increase inductance.  If the Tune-C spitting decreases, an 
increase in L-sup is indicated -- i.e., winding a new L-sup with more 
inductance.  .  However, R-sup needs to have approx. as many Ohms as 
L-sup., so a change in both may be needed at some point.   
  . 
>> Carl, KM1H, suggested removing all of the mods you did and seeing how 
>> it works.  Perhaps something is amiss with them.  If something is not 
>> assembled correctly on the input circuitry, you could be creating an 
>> instability there as well.  This is probably not a bad idea.  Then 
>> reinstall the mods one at a time and try to determine where the problem 
>> occured.
>> 
>> Hope this helps.
>> 
>> 73,
>> 
>> Jon
>> KE9NA
>Jon,
>I read that Carl suggested removing mods to go "original",
>but following the input circuit changes per Rich's suggestions
>to reduce VSWR (reducing coil windings and changing in/out caps)
>is pretty hard to undo. 

indeed, Jon, and for what?.  .  The idea that input SWR could be 
significantly related to intermittent Tune-C arcing is not reasonable.  
One of the nagging problems with parasites is that they are seemingly 
female, and thusly can change their minds at any time. 
 .  As Murphy said:  Some things are more complicated than they look.  

-  later, Bennett

Rich. Measures.  Web site:  www.vcnet.com/measures


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