>It seems to me that even a 100% increase in Rs would not make much
>difference in the performance of a VHF parasitic suppressor.
Depends on the amp. The Clipperton L and the Ameritron 811 series do not
like much of a value change. The SB-220 is still happy at 100 Ohms.
>>With overstressed 2W carbons for R, I agree. But with 5W metal oxide
>>available at a fraction of the cost of 2W carbons why not change when
>the
>>cover is off? If you want to spend the time measuring the R of an
>>antique, why not just upgrade at the same time? I dont even bother
>>wasting my time to measure the old ones any longer.
>>
> Is it a waste of time to measure the resistance of a
>seemingly-critical
>resistor?
In my case...yes. I have already measured enough of them to see the
pattern. Since time is money I cant see wasting it. With Mouser selling
5W metal oxides at $ .49 it makes no sense to unwind the L measure the R,
rewind the L and put it back in the circuit only to wonder when you will
have to do it all over again.
. . There are two types of damage to Rs. It is my
>opinion
>that when there is cosmetic damage and less than a 50% change in
>resistance, 28MHz operation is usually the reason.
Cosmetic damage and any increase up to 10 times or more is usually from
CB or 10M use. The increase depends how many hours or years of abuse.
However, if there
>is
>little or no cosmetic damage, and a large increase in resistance,
>higher
>frequency energy is the culprit.
During the debug of a new amp I agree. In a well behaved amp that just
went bang I disagree. Take a 2W carbon and subject it to a 100X overload
for a few milliseconds at DC. You will see the same results. Many of
those seemingly unblemished resistors will have a hairline crack and you
can snap them apart with your fingers. If the crack did not extend to the
outer rim you should still be able to snap them. You cant snap a good 2W
carbon unless you are a 300 lb gorilla.
73 Carl KM1H
>
>cheers
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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>
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