[Hammarlund] sp600 frequency question

[Al Parker]

Hi Eugene,
    Don't worry abt a freq. counter unless you need it to know what freq.
your sig. gen is on.  To get the freq.s right, do the alignment of the HF
osc. secn, you'll need a long thin tuning wand with a straight screwdriver
end, to get down thru the RF deck to the coil & cap adjustments in the
turret (helps if it's got a recessed end for the coil slugs).  Takes some
getting used to to get it on the cap or slug, rocking the bandswitch knob
might help a little to get it on, you're going down thru 2 tight holes.
It's a lot of back & forth motion end to end on each band, but unless
somebody's bent plates on the tuning variable, you should be able to get
it so it won't be out more than a pointer width anywhere, and a lot closer
in lotsa the dial.  Also do the whole RF & IF alignment, you'll probably
be surprized how much better it gets.  (but you WILL have to get to those
BBOD's sometime, they'll fail 1 by 1 & work you to death.)   Just follow
the manual instructions for the alignment, connect your AC voltmeter to
the audio output, don't worry abt it's calibration, you're just tuning for
peak.  Don't worry abt the alternate scope procedure, you can get darn
good without it.
    It's not a freq. meter, it's a great bandcruiser for SW listening, can
copy SSB with the right technique, even up on 10m.  I've listened to the
net on 14.300 for hours without any adjustments exc. for RF gain.
    Move the tap on the pwr xfmr from 115 to 125v, if you haven't already.
    You can do the whole thing in a few hours of enjoyment.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info

----- Original Message ----- 
From: "Eugene Hertz" <ehertz at tcaf.org>
To: <hammarlund at mailman.qth.net>
Sent: Saturday, March 19, 2005 7:32 PM
Subject: [Hammarlund] sp600 frequency question


hello all,

I have never aligned a radio in my life, but as soon as my RF generator
arrives in the mail I might take on the sp600-jx26.  Here's whats up.

I noticed that the dial was off when tuning to wwv 15Mhz (I think the log
scale read 25 instead of 0 that I guess I would expect) so I connected a
frequency counter (actually tried two different counters) to the HFO 6C4
on the grid pin with a 5pf cap to remove the dc.

What I noticed on both freq counters was when I received the *strongest*
signal both in sound and in s-meter the freq counter was off (in other
words, one would expect the counter to show 15Mhz+3.955Mhz IF or
18.955Mhz. In actuality it read something like (didnt write it down but
you'll get the idea) 18.990 or about 30kHz off. I dont actually remember
how much off, could have been 5khz or something. I'll check again if it is
material to the discussion.

So what does this mean? Does it mean the center of the bandpass for the if
filter is off somehow? meaning I get a loud signal somewhere off the
center? Or could it be the 5pf coupling cap that is throwing off the freq
counters?  Could the dial being off be somehow involved with this?

Should I stop with this foolishness and just start a realignment process?
(by the way, how hard is it? I have yet to read the process in the
manual-not even sure if the process is in the manual! I can use a freq
counter, o'scope and (once it arrives) an rf generator.  How many days
should I plan for this? I have some black beauties but if I can avoid it,
I would rather not touch them for fear of causing more damage. The radio
seems to work rather well at the moment, just perhaps slightly off on
frequency.

thanks!
Eugene




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