[R-390] 0.5-8.0 Low Sensitivity (Long)

Mon Sep 11 14:13:16 EDT 2006

All this talk makes me more interested in my R390As than it has in some 
time.  The current project didn't look like I'd ever get it back together 
and working very well at all, but this last weekend saw me getting very 
good results after working on the crystal/RF decks.  Signals were really 
coming in strong last night even in the part of the year where the bands 
are usually full of static.  Fun.

I was thinking of selling these when I'm finished with the current one, but 
now I'm not so sure.  It's always a lot more fun when you get a little 
reward for your efforts.  If I can get this IF deck working properly, this 
should be a very nice radio.

Barry - N4BUQ

On Mon, 11 Sep 2006 13:25:52 -0400, "dmartin" <dmartin at visuallink.com> 
wrote :

> I do a pretty "classic" 1st IF alignment - peaking the slugs back-to-
front at 1.2 megs 
> and then peak the trimmers back-to-front at 7.6 megs, with signal input 
at the 
> balanced antenna connector, one pin grounded. No, I've never tried to 
screw the slugs 
> back in (or out!) to see if doing so would enable a two-peak trim cap. 
I'm sure the 
> diode load VDC would drop off if I moved the slugs from wherever 
their "natural" 1.2 
> meg peak is, though. However, Todd and a couple of other private replies 
have 
> suggested this so maybe I'll play around with it tonight. 
> 
> To Cecil's point, it >does< seem to me that if I wanted to go nuts over 
not getting 
> two peaks on every trimmer the only recourse might be to start 
empirically adding a 
> little fixed capacitance, above what is factory original. The 1st IF uses 
51 (I 
> replaced with a 50 pF)and 68 pF and the can in question is the one with 
50 pF. CDE 
> makes a 56 pF. I could try that, or parallel other combinations. 
Experimenting like 
> this wouldn't be too bad in the 2nd IF and RF, where the fixed caps are 
all pretty 
> much in the easily accessible cans. Bit of a drag to do that in the 1st 
IF though, 
> where the fixed caps are under the deck. Be good to hit that one right 
the first time! 
> I've had rf decks out a bunch of times over the years. It's kind of like 
mowing your 
> yard in August - not hard, just takes awhile and you don't look forward 
to it!
> 
> Let's see what other posts come in. It is taking well under 4 uV for -7.0 
VDC diode 
> load voltage on 0.5-8.0 frequencies right now, which is TM-spec for field 
checking 
> sensitivity. That's from my not necessarily calibrated HP-606 with no 
effort at 
> impedance matching. Point is, sensitivity seems fine, but I do wonder 
what else might 
> be available ???
> 
> I haven't decided whether to get paranoid about going for two peaks on 
all the 
> trimmers (could be fun!) or just move it from the bench to my radio desk 
and enjoy it!
> 
> Dan
> WB4GRA
> 
> --
> Open WebMail Project (http://openwebmail.org)
> 
> 
> ---------- Original Message -----------
> From: "Cecil Acuff" <chacuff at cableone.net>
> To: <ToddRoberts2001 at aol.com>, <r-390 at mailman.qth.net>
> Sent: Mon, 11 Sep 2006 10:12:44 -0500
> Subject: Re: [R-390] 0.5-8.0 Low Sensitivity (Long)
> 
> > Well that's another tip off that there is a resonance problem in that 
> > particular tuned circuit.  The slug tuning should never be at it's 
threaded 
> > limit to achieve the peak....(it's actually not the peak because you 
are at 
> > a physical limit prior to reaching the peak)
> > 
> > I've had to add and sometimes even remove fixed capacitance to get 
within 
> > the range of the trimmer.  It's seems to me the inductance value has 
changed 
> > from when the can was manufactured.  Maybe there is fine particles of 
slug 
> > material worn into the coil form.  Maybe the slug has a chunk missing 
off 
> > the bottom of it...who knows.  The factory value of the fixed mica cap 
is no 
> > longer correct and requires custom matching to the current circuit 
> > conditions.  I've had to do it several times and sometimes the effect 
on 
> > performance is dramatic because you don't know how far off of the real 
peak 
> > you are until you can achieve two distinct peaks with the trimmer 
capacitor 
> > at different positions in their rotational range.  It's worth the 
effort....
> > 
> > Cecil...
> > ----- Original Message ----- 
> > From: <ToddRoberts2001 at aol.com>
> > To: <r-390 at mailman.qth.net>
> > Sent: Monday, September 11, 2006 9:59 AM
> > Subject: Re: [R-390] 0.5-8.0 Low Sensitivity (Long)
> > 
> > >
> > > All else works fine now and I'm tempted to just leave well enough 
alone.
> > > However, I'm
> > > puzzled why fresh trimmers and new micas at spec values cannot get 
two 
> > > peaks
> > > during
> > > alignment.
> > >
> > > Got any ideas?
> > >
> > > Dan
> > > WB4GRA
> > >
> > > Have you tried screwing in the slugs a few more turns? What happens 
when 
> > > you
> > > screw in the slugs a few more turns? Does the signal continue to peak 
or 
> > > does
> > > it start to fall off? If it starts to fall off then the single peak 
would
> > > appear to be near correct even though you only get one peak when the 
slug 
> > > is
> > > maxxed out. I wouldn't worry too much about a single peak if the 
> > > sensitivity is
> > > back to normal. 73 Todd WD4NGG
> > > _____________________________________________________________
> 
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