[Hammarlund] SP-600 question

[Al Parker]

Hi Gary,
    I know the feeling.  I've had a similar problem in one recently.  The
fact that the RF gain ctrl won't have any influence is because in the AVC
posn, it's acting thru a 3.3 megohm resistor to the AVC line.  If the AVC
line, for some reason, is acting like it's abt 100kohms, that's what
you'll get.  In your case that is changing, probably due to a leaky cap.
In my case, after a lot of searching, it turned out to be a mica cap in
the xtal phaisng can, that was abt 70kohms to gnd.  Don't let anyone ever
tell you that micas don't fail.  I've had 2 in the last few mo.s, one in a
Collins, and 1 in an SP-600.  Had 2 others in the previous cupla yrs, both
in Hammarlunds (that's probably over 50% of the brands I work on).
    If you take resistance readings in each AVC chain of resistors toward
each IF xfmr that gets AVC, you should be able to see where the resistance
gets lower as you go towards the can.  That's where the culprit is.  It
should be closer to infinite to gnd when you get to the grid of the tube.
    To get a look at the other problems in this particular SP-600, you can
take a look at:
http://www.thecompendium.net/radio/SP600sn4706.htm
    Pse let us know what you find.  We've been enjoying your reports.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info


----- Original Message ----- 
From: "GBrown" <gkbrown at gwi.net>
To: <hammarlund at mailman.qth.net>
Sent: Tuesday, April 26, 2005 6:33 PM
Subject: [Hammarlund] SP-600 question


> OK, for you guru's out there. I have a head scratcher. Receiver is a
> SP-600JX. The early one. Now, it was working great and now there is no
> control on the rf gain in avc position. I dug thru all the caps and
> resistors, replace tubes with no result. What happens is, if you turn it
> off, wait awhile and turn it back on, it works great in avc position. If
I
> throw the switch into manual position then back to avc, volume is full
> blast, no avc action no matter where you turn the control. put it back
in
> man position and it acts normal. Switch tests fine. Any one out there
mite
> head me in another direction. I have been all over the avc circuit and
> subbed in new electrolytics in place of the bath tubs. I am at a stand
> still.
> Regards,
> Gary...WZ1M
>
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