[Heath] More on the SB-303 Noise Blanker
N4ch at aol.com
N4ch at aol.com
Sat Mar 15 06:55:07 EDT 2014
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.
73, Herman, N4CH.
In a message dated 3/14/2014 2:30:27 P.M. Eastern Daylight Time,
pbrickey at verizon.net writes:
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.
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