[Hallicrafters] Best Rx?

[Robert Nickels]

On 11/29/2010 9:20 AM, Mark K3MSB wrote:
> Does Moore's book show a picture of this early version?
>
Raymond Moores book only includes a generic picture of the SX-111, along 
with the information that I summarized.  To be more specific, the tube 
complement of the early version does not include any tube designated as 
being for a crystal calibrator.

For the later version Moore gives the following description:  "Tubes 
-13, including 6AU6 calib.  REMARKS:  Adds crystal calibrator to 
original SX-111".

I hope this explanation is sufficient.  While I don't know for sure, the 
logical conclusion is that the calibrator switch and socket were 
provided for, but the module itself was not installed - a simple plug-in 
addition that was made in the later production version.

Some time ago I was fortunate to acquire a large quantity of original 
Hallicrafters manuals and other documents from a former employee.  Some 
interesting reading for sure, including the original manuals for the 
HT-36 and SX-112.   While I didn't see anything specific to the 
calibrator in the original SX-111 manual, there is an Errata Sheet 
tucked in the back (Form # 094-902331 for you inquiring minds out there) 
- that may be of interest as it details several changes:

1.  A design change was made to the S meter circuit so it would indicate 
relative signal strength when the RF gain is in positions other than 
maximum clockwise.   As a result the owner is advised to disregard such 
references in the printed manual.

2.  "The Pointer Reset control was modified from a mechanical to an 
electrical type reset to improve dial calibration accuracy.   See the 
partial schematic below...."    (shows addition of C-86, a 3-17uuf 
trimmer cap connected in series with C85 (6 uuf) to pin 8 of SW1F and to 
one end of C83, a 51uuf N300 capacitor).

(So the next question is - has anyone seen an early SX-111 or prototype 
model that has the mechanical Pointer Reset?)

3.  AVC, Dectector, and ANL Stage:  describes a modification to V5 "to 
improve performance".    I will reproduce this step verbatim for the 
benefit of anyone wishing to check their own SX-111 schematic to see if 
it has been incorporated.

     a.  Delete the 150V regulated lead which goes to pin #3 of V4 
(6BJ7).  The lead is located between the junction of S6 (BFO switch) and 
pin 1 of V8 (OA2, Voltage Regulator) and C84 (.02 uf Capacitor).

     b.  Add an internal shield (pin #3) to ground in the schematic 
representation of V5 (6BJ7).

The above form was to be packed with Instruction Manual 094-902032, 
which is that of the copy I have, which is also marked "659" which 
logically indicates a publication date of June 1959.   Just for grins I 
looked at QST ads for the last half of 1959 - it was a  busy year for 
new product introductions at Hallicrafters.   The S-107, S-108, SX-110, 
and latest version S-38 all debuted in September, as well as the 
HT-37.    But it wasn't until the November issue that the "Throroughbred 
New SX-111" appeared:

"The team that designed the famous SX-101 now brings you an entirely new 
class of precision receiver at a moderate price".  Included in the 
features listing is the following:   "10 tubes plus voltage regulator 
and rectifier", but the next bullet says "built-in crystal calibrator, 
48:1 tuning ratio".      A typo?  Regardless,  you couldn't have a 
calibrator without adding that 13th tube!

73, Bob W9RAN