Tom, Between the SB-220 amps I have owned and worked on for repair, the
number is staggering. I can tell you with certainty that many of the Sb-220's
I
have seen have had their relays wired 2 different ways. It really doesn't
make much difference electrically since the difference is in which sets of the
3 poles on the relay does the antenna switching. Either way it works. I
often wondered why I have seen the 2 distinct ways of wiring the relay. I
thought perhaps some people just "did their own thing" with that, but now it
would
make sense that at some time Heath changed the assembly manual from one way
to the other and therefore the field difference. Most likely there was a
change but I don't know when it occurred. I thought that my experience with
seeing so many of these amps and noticing that fact would support the idea
that
a change was made in the wiring at some point. On another note, since I
have seen SO MANY SB-220 amps in the past 40 years as a ham, I can tell you
again with certainty that about 7 out of 10 SB-220 amps out there have one or
more burnt band switch contacts. JUST BECAUSE THE AMP "WORKS" DOES NOT MEAN
IT
DOES NOT HAVE A BAD CONTACT OR MORE. Since the band switch contacts are
redundant, a set of contacts can be absolutely toasted and the amp could still
work on 15 or 10 meters (usually the ones that are toasted). I'd say if you
bought a used SB-220 you have a 30% chance that the band switch is 100% AOK.
Not good odds. It is nearly impossible to check the inside set of contacts on
the band switch with the switch installed in the amp. The outer contacts
can be seen with a flash light and an inspection mirror. Fortunately the
outer contact seem to go first and can be seen on close inspection, but
sometimes not. If a fussy buyer of a used SB-220 was to insist that the band
switch
be 100%, there would be a bargain basement price on many of them. But often
since they do still work they are taken for regular sale price. Off the soap
box. 73 Lou
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