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<DIV><FONT size=4>Sounds like you might have a REALLY rare and unique SB-303, if
it is indeed "factory". The SB-303 receiver was never offered with a
blanker (either "standard" or as an option), as far as I know. It
might be that during the engineering development of this receiver, having a
noise blanker was contemplated, but this idea may have been scuttled just before
the product was finished, released, and sold. If this is indeed the
case, I suspect that if a noise blanker once resided in your '303, it was
probably a bit different from the "production" blankers that were sold for the
SB-104/A transceivers, which were first released some 3-4 years after the '303
was initially offered. Perhaps your SB-303 is a blanker-equipped
engineering sample/prototype (but with the blanker removed). I'm
99.999% sure that all "factory" SB-303 receivers that Heath actually sold and
shipped had an attenuator control instead of the blanker (and its
control). One other possibility: your SB-303 might be a "standard"
production receiver, and whoever added a blanker to it (but later it was
removed from your particular receiver) may have had the front panel
professionally re-lettered, making it "look factory". Try looking at
some of the date codes on some components inside your SB-303. If all
are 1971 (and a bit earlier), you may indeed have a prototype receiver that
was wired to accept a blanker Heath may have been considering at the time it was
put together, probably in Benton Harbor. If most of the date codes
are 1974 (and later), you probably have a "production" receiver that someone
modified to accept a SB-104 accessory blanker (and did a nice job re-lettering
the front panel).</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>The copy of the SB-303 manual you have sounds interesting, in
that it includes a blanker. Possibly it is a "proof-build" manual
for a small group of pre-release SB-303s that may have actually gotten to this
stage before the blanker idea was dropped, or (more likely) someone made a copy
of the SB-104's accessory blanker kit manual, and included it with a
"production" SB-303 manual you own........? Hard to even
guess without actually seeing what you have. The two "NB"
markings on your SB-303's mixer board may indeed be in ALL SB-303s........I've
not taken mine apart to see if such markings are there, but these might be
"artifacts" from the days when such an option was being considered (if indeed a
blanker was ever thought to be offered), and then dropped. Trying to
nail down a time where the example U have was assembled is not an exact science
either........a handful of components (with date codes) could have been changed
over the last 40 years.</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Good luck.</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>73, Herman, N4CH.</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV> </DIV>
<DIV>
<DIV>In a message dated 3/14/2014 2:30:27 P.M. Eastern Daylight Time,
pbrickey@verizon.net writes:</DIV>
<BLOCKQUOTE
style="BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px"><FONT
style="BACKGROUND-COLOR: transparent" color=#000000 size=2
face=Arial>Hi,<BR> I think that I had better clarify my first
Email. My SB-303 has a factory labeled front panel which has a labeled
Noise Blanker<BR>control where the RF Attenuator control is located. My
manual (a copy) has instructions for assembling the noise blanker board
which has a part number 85-350-2 and is not a small board as it has an IC
(CA3012), 6 diodes, and 5 transistors. The Mixer board has labels on 2
pins labeled NB. The noise blanker control is a 10K linear control with
a switch. I looked in my 1971 catalogue where the SB-303 is first
presented and there is no mention of a noise blanker, however, in the picture
of the receiver one can see that the control on the lower right has had its
label blanked out. <BR> So, I assume that the SB-303 was initially
set up with a noise blanker, but that for some reason it was not incorporated
in the finished product.<BR><BR> 73's<BR>
Peter
K6dgh<BR>_______________________________________________<BR>Heath mailing
list<BR>Heath@puck.nether.net<BR>https://puck.nether.net/mailman/listinfo/heath<BR></FONT></BLOCKQUOTE></DIV></FONT></BODY></HTML>