> AT 10:43 AM 5/19/98 EDT, you wrote:
>>Both. But the amps I witnessed were not SB-220's or had 3-500Z's.
>>I would still prefer to stick to the SB-220 and related clones since
>they
>>are so popular and the majority of readers can relate to them.
>Roughly 4
>>out of 10 SB-220's that I buy have some sort of switch damage...which
>is
>>why they are for sale...cheap. In almost every case, the owners say
>the
>>amp was tuned and operating perfectly fine and the switch arced for
>no
>>obvious reason.
>
>Carl, is it possible that in some of those cases, at least, the switch
>arced because of wear in the indexing mechanism? I mention this
>because my
>SB-220's bandswitch feels as if it has developed a certain amount of
>play,
>and might be prone to being "almost" in one position or another.
>After
>all, these things are getting pretty old!
The above received privately so I deleted the header.
Some of the failures have been due to loss of tension in the contacts.
These show up slowly over time and appear to be due to heat as the
contact resistance builds up.
Those failures do not appear to be catostrophic,and usually affect only
one of the parallel set of contacts.
OTOH, the "other" failure leaves a mess of evaporated metal and material
all over the ceramic. They also involve 2 adjacent contacts.
The switch detent is pretty rugged and I have yet to see a purely
mechanical failure. What should be checked is the mounting of the plate
wafer. If any of its support hardware to the shield is loose it could
cause an alignment problem.
73 Carl KM1H
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