[Hallicrafters] SR-150 problem

[Kenneth D. Grimm, K4XL]

> I wonder if you SR-150 owners have ever run into a strange problem
with
> the receive audio.  The audio is raspy sounding.  Even the 100kc
calib.
> tone is not pure.  The audio sounds as if it is rapidly pulsing, not
> quite distortion in the usual since.  Now I know that the first thing
to
> check is the filters in the power supply and all the electrolytic caps
> in the transceiver, check the tubes, voltage check at each pin,
> resistance check at each pin,  good speaker etc.  I even ran it on two
> other PS-150 power supplies.  Same problem.  This is not distortion
> caused by hum.  I have an idea that an oscillation is getting into the
> receive audio string somewhere and is beating with the BFO.


I agree with Wayne, WB4OGM.  This sounds like motorboating in the AVC.
My gut feeling is that you will find a problem with a grid load resistor
in the AVC line.  Check R89, 90, 92 and 93 for a start.
Since the problem is on receive only, this would be a great time to have
a signal tracer.  If you have one, start at the audio output (V13) and
move back to the 1st audio (V11A).  If you don't have one now, you might
consider adding one to your service gear.  They can be picked up a flea
fests for $20-$30 these days, and at that price they are a "must have"
piece of equipment.  That is, unless you do all of your servicing with a
scope.   8^)

While I was looking at the schematic for the SR-150, I discovered that
the right hand edge of the right hand page in the BAMA collection is
missing.  It would be great if someone could scan that part of the
schematic and upload it.  I take full blame for sloppy scanning on this
one.  Gary Harmon went to the trouble and expense of sending the manual
to me for scanning and then I screwed it up!  And on the schematic, no
less!!!

I am told
> by on the air contacts that the transmitted audio is fine with no
trace
> of ripple or distortion.  This thing just about has me stumped.  I
have
> had this rig since it was new and it just turned forty.  Anyone have a
> suggestion?
>
> Burt Pratt
> K4PRF
> pratt at zebra.net

Ken K4XL
k4xl at arrl.net
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