[Hammarlund] IT SINGS THE OLDIES!

[Al Parker]

Hi Phil,
    Sounds good, it's hard to strip something down & redesign it if it
starts working without too much effort.  These old beasts just find it
hard to give up.
    Keep up the good work.  I"ve got a similar hulk of an SP-600 sitting
under my bench, I oughta get after it one of these days.  It's had some
"added features" tacked in there, missing sidepanel, etc.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info

----- Original Message ----- 
From: "Philip Atchley" <beaconeer at sbcglobal.net>
To: <hammarlund at mailman.qth.net>
Sent: Thursday, July 14, 2005 6:30 PM
Subject: [Hammarlund] IT SINGS THE OLDIES!


> Hi All,
>
> Remember that SP-600 that arrived here, literally a basket case, with a
> totally stripped chassis, tube sockets and IF cans in baggies etc, along
with
> my intent to rebuild it from scratch?
>
> Well, today it got to the preliminary testing stage.
>
> Today, after quickly buzzing it out to make sure there weren't any B+
shorts
> or anything, I got brave and applied power.  First without the 5R4
rectifier
> in place (to check bias and filaments etc).
>
> All ok there, so I plugged the 5R4 in, put an antenna on it and checked
around
> the BCB.  Alas, no stations, but no smoke either ;-)  I tested the audio
> section for buzz when I touched the volume control with a test lead,
that was
> ok! Not even normal IF background noise though, indicating either the
detector
> or an IF stage was dead.  I connected a lead to the 455KC output on the
other
> SP-600 figuring I'd use it as a signal source, starting at the detector
and
> working my way back.
>
> I heard it at the detector, so kept moving back through the circuit, I
could
> poke the signal all the way through the IF strip, but couldn't determine
if
> the stages had any real gain (it doesn't yet have an "S" meter
installed).
>
> Then I thought, hmm. . .  Perhaps the signal from the good SP-600 IF
output
> was
> just too strong.  So, I turned it's RF gain down, the volume all the way
up,
> and then turned the RF gain up just barely enough to hear a weak signal
in the
> speaker.  Again I went through the IF strip, this time as I went back a
stage
> I could hear the differences in level.  I peaked each stage as I went,
most
> were way out.  When I got finished I removed the test signal, and Voila!
I
> had RF noise!  Putting an antenna on the radio it came to life with
signals
> all across the BCB.  The selectivity switch worked as expected.
>
> Right now I have it over on the other side of the room playing the
oldies
> station through a headset, just to burn it in awhile.  I think the AGC
section
> needs more work as AGC voltage seems a little lower than I think it
should be.
> That could be a bad tube or other component (or a wrong wire somewhere),
or
> something else dragging the gain down, but all tubes were tested prior
to
> installing them.
>
> But at least there is life in the old carcass, and I'll bet that is the
first
> time in many, 'many' years that any electrons have flowed through any of
those
> parts
> too!  ALL resistors, paper caps, lytics etc are new.
>
>
> 73 de Phil,  KO6BB
> 991 Different NDB's heard to date.
> SWL QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
> THE BEACONEER'S LAIR:    http://www.geocities.com/ko6bb/
> Merced, Central California, 37.3N  120.48W  CM97sh
>