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<DIV>I just reviewed quickly two of my original SB-303 manuals (595-1124 and
595-1124-01)</DIV>
<DIV>In manual 595-1124 (the 1st iteration of the manual) there is no reference
to a "noise blanker" except on page 152 Troubleshooting Chart for the Mixer
Circuit Board. Symptom: No output from the first mixer; Possible Cause: 2.
Refer to the "Blanker Troubleshooting Chart." There is no Blanker
Troubleshooting Chart in the manual.</DIV>
<DIV> </DIV>
<DIV>In manual 595-1124-01, page 152 Troubleshooting Chart for the Mixer Circuit
Board. Symptom: No output from the first mixer; Possible Cause: #2 no
longer appears.</DIV>
<DIV> </DIV>
<DIV>And, as I said in another post, the SB-104 noise blanker (SBA-104-1)
schematic does not match the schematic you have for your SB-303.</DIV>
<DIV> </DIV>
<DIV>Pete, wa2cwa</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>On Sat, 15 Mar 2014 06:55:07 -0400 (EDT) <A
href="mailto:N4ch@aol.com">N4ch@aol.com</A> writes:</DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 10px; MARGIN-LEFT: 10px; BORDER-LEFT: #000000 2px solid"
dir=ltr>
<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="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><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>
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