[Hallicrafters] SX-117 Help

[Koehl_House]

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


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