[Hallicrafters] SX-117 Help

Sun Sep 15 12:24:19 EDT 2002

What's the chances I can get a copy of that article? I would lke to change
one of the 117's I have any do a side-by-side.
..'course I probably have enough info to do that already....yeah.

Tnx, Bill, keep hunting.

73, Dick K9FFK

 -----Original Message-----
 From: Bill Smith [mailto:billsmith at ispwest.com]
 Sent: Sunday, September 15, 2002 10:46 AM
 To: Koehl_House; hallicrafters at mailman.qth.net
 Subject: Re: [Hallicrafters] SX-117 Help

 The plot thickens..

 I rooted through the equipment archives at the Hamilton Wireless
 Association's clubhouse, and lo and behold, found an updated schematic that
 represents the wiring in this receiver.  To quote:

 "Prior to production but after the Handbook was printed, certain wiring and
 component changes were made in the Model SX-117 Receiver to improve its
 performance.

 These changes are contained in the schematic diagram and parts list herein
 enclosed.  Please discard the schematic diagrams and parts list
 contained in
 the Handbook and refer to those contained within this sheet whenever
 necessary."

 I have only made a cursory review of the two schematics, but changes
 identified so far are:

 1.  Change 1st mixer to a triode configuration.
 2.  AVC detector bias 1 Meg R63 changed to 6.8 Meg
 3.  AVC Time constant adjusted in C107 changed from 0.47 to 0.22 Mfd.
 4.  Grid of AVC amplifier V10A was connected to V9, 6BA6, is now connected
 to the IF transformer following 3rd mixer V8A, 6EA8.  Coupling
 capacitor C75
 0.001 is now C65 100pf.  The old C65 was removed.
 5.  Selectivity resistors R85 and R87 were changed from 470 ohms to 390
 ohms.

 Sensitivity in this receiver seems on a par with the TS-440, but S-meter
 readings are still about 20 db below that of the Kenwood.

 73 de Bill, AB6MT
 billsmith at ispwest.com

 ----- Original Message -----
 From: "Koehl_House" <erkoehl at attbi.com>
 To: "Bill Smith" <billsmith at ispwest.com>; <hallicrafters at mailman.qth.net>
 Sent: Saturday, September 14, 2002 2:39 PM
 Subject: RE: [Hallicrafters] SX-117 Help

 > I have two SX-117's, acquired years apart, both wired per
 factory diagram.
 > Both working nicely. Although, I have not checked everywhere, I have not
 > heard of a factory mod or a user mod of this nature. Looks like someone
 was
 > carefully improving on the receiver noise...triode mixers are quieter.
 > I had a stereo record player, that once had a popping audio problem. It
 > would also produce a 'frying bacon sound'....faulty output transformer.
 > The AVC is routed through the gain control to V7, the 1650 kHz IF
 amp...Bad
 > control, faulty components means low gain from V7. It could be that the
 AVC
 > voltage is too high thus shutting things down. What have you for
 resistance
 > and voltages at V10 and V7?
 >
 > In the wondering out loud department in my head.... What would happen if
 you
 > shunt a 100K to 1 M resistor from AVC to ground? (Or better yet, tack the
 1
 > meg across the 6.8 meg.) more signal? If yes return AVC to factory wired
 > version. That 6.8 Meg forms a divider with R64, 220K. You should have
 about
 > 24 Vdc at V10-2.
 > Also wondering out loud...Would a 'triode wired' 1st Mixer have as much
 > conversion gain as the pentode version? If not, then the higher value R63
 > may be an attempt to compensate for that? The lower value for C107 will
 > decrease the AVC time constant...maybe just a 'personal
 preference thing'.
 >
 > another thought...AVC only goes to two stages, V1-1, V7-2. If voltages
 there
 > are acceptable, then something else in the signal path is not doing it's
 job
 > thus causing a low AVC, and low signal. (There's a catch-all disclaimer,
 > eh!) I had a similar problem until I changed the 6EA8's, V2 and V8.
 >
 > staying tuned...
 >
 > 73, Dick K9FFK
 >
 >  -----Original Message-----
 >  From: hallicrafters-admin at mailman.qth.net
 >  [mailto:hallicrafters-admin at mailman.qth.net]On Behalf Of Bill Smith
 >  Sent: Friday, September 13, 2002 8:07 PM
 >  To: hallicrafters at mailman.qth.net
 >  Subject: [Hallicrafters] SX-117 Help
 >
 >
 >  I just acquired a SX-117,  which, after replacement of the trim
 >  capacitor on
 >  the VFO,  seems to be working correctly... except for popping audio
 noises
 >  in loud signals (AVC problem?), generally weak sensitivity on all
 >  bands, and
 >  an S-meter that won't move above S-9 on any signal.  I've
 checked through
 >  the AVC and everything seems to ok in that circuitry.
 >
 >  I am using the manual available online, and have found a number of
 >  discrepancies between the schematic and what is in the receiver.  For
 >  example, in the AVC line, R63 is listed as 1meg in the manual, but is
 >  6.8megs in the receiver.  C107 is listed in the manual as 0.47 mfd, but
 is
 >  0.22 in the receiver.
 >
 >  Looking further, it looks like the first converter, which appears to be
 >  triode-connected in the receiver (a 470 ohm resistor is wired between
 plate
 >  and screen of V2A) is shown in the schematic with the screen
 bypassed and
 >  connected to the B+ through a screen dropping resistor.
 >
 >  I haven't checked the rest of the set, but it looks like factory
 revisions
 >  were made to production runs.  Has anyone run down the changes made in
 the
 >  circuitry, or have any experience with the problems describe above?  I
 note
 >  the set has an aluminum chassis, but grounding seems ok from the few
 tests
 >  made so far.
 >
 >  Thanks in advance!
 >
 >  73 de Bill, AB6MT
 >  billsmith at ispwest.com
 >
 >
 >  _______________________________________________
 >  List Administrator: Duane Fischer, W8DBF **for assistance**
 >  dfischer at usol.com
 >  ----
 >  Hallicrafters Collectors International: http://www.w9wze.org
 >  ----
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 >
 >