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>> Subject: Re: [AMPS] SB-220 TUNE Cap Arcing
To: <amps@contesting.com>
>> 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>
>> cc: "amps@contesting.com" <amps@contesting.com>
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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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