[Heath] More on the SB-303 Noise Blanker

[pmarkavage at juno.com]

I just reviewed quickly two of my original SB-303 manuals (595-1124 and
595-1124-01)
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.

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.

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.

Pete, wa2cwa


On Sat, 15 Mar 2014 06:55:07 -0400 (EDT) N4ch at aol.com writes:
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).

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.

Good luck.

73, Herman, N4CH.


In a message dated 3/14/2014 2:30:27 P.M. Eastern Daylight Time,
pbrickey at verizon.net writes:
Hi,
  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
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. 
   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.

  73's
            Peter    K6dgh
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