They are wired into this spot. I have had several SB-220s and the assembly
instructions have you install them this way. They are also depicted this way
on the original schematic.
All the amplifiers that I know of, don't change the fuse sizes when you
convert from 120 to 240 volts. The Ameritron is the exception to this rule.
As I remember, the AL80 and SB-1000 change fuse sizes.
The fuses and circuit breakers are for short circuit conditions. No
necessarily slow overloads.
73
Jim W7RY
----- Original Message -----
From: "kingwood" <k5jv@kingwoodcable.com>
To: "Amp Reflector" <amps@contesting.com>
Sent: Saturday, December 27, 2008 11:06 AM
Subject: [Amps] SB-220 schematic error
> Greetings to all,
>
> I wrote this for Tom, K0KDG, and then decided is relevant to the
> entire group. So, enjoy, or destroy.
>
> 73 de K5JV
>
>
> Tom,
>
> I just ran across your wonderful SB-220 page. You did a great job
> with this information. It is, and will continue to be, a great help to
> the
> Ham community for years to come.
>
> However, I want to point out one very important possible oversight
> that, I think, is very important. The SB-220 schematic you show has a
> very
> glaring error. It shows the AC circuit breakers in the wrong place, It
> shows them to be in the main AC line which would require different values
> of
> CB/fuse when switching between 120 and 240 VAC power. The CB's should be
> on
> the other side of the voltage selector strip, thus placing them in one of
> the individual transformer primaries, not the main AC line, which feeds
> both
> primaries. This way, the CB's do not have to be changes when switching
> between 120 and 240 VAC power because they are only protecting one of the
> transformer primaries each ( always the same whether the primaries are in
> series, or parallel.
>
> Heath published this error, back in the 70's, in only one series of
> the SB-220 manual. This incorrect schematic is, unfortunately, the one
> that
> is used most often in modern articles. I immediately notified them about
> it, along with many other avid SB-220 users and maintainers. They
> immediately publish a correction notice and changed all subsequent
> printings
> of the SB-220 manual. However, the harm was done because hundreds of
> SB-220
> were sold with this incorrect schematic.
>
> Nearly every article I have seen about the SB-220 power supply, in
> recent years, shows this incorrect schematic. This subject is always
> great
> for a rousing discussion among 75 meter Amplifier Groups. The question
> always comes up from new people, "why does Heath and Kenwood (among other
> manufacturers) not change the value of fuse/CB protection when changing
> between 120 and 240 VAC operation". Kenwood, in their TL-922 manual,
> gives
> the best explanation for this hookup, even with current flow diagrams.
>
> Tom, I do not mean anything I have said here to be, in the least
> bit, critical of your great effort. I repair amps all day, every day.
> Not
> a month goes by that I do not get an amp in for major repair because the
> owner doubled the size of the fuses when switching from 240 to 120 VAC
> power
> and then cooking them.
>
> 73 de K5JV
>
> Lon W. Cottingham
> 1110 Golden Bear Ln.
> Kingwood, TX 77339
>
> 281-358-4207
> 281-358-4234 FAX
> 281-795-1335 Cell
> k5jv@kingwoodcable.com
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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