[Heath] More on the SB-303 Noise Blanker

[N4ch at aol.com]

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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