[Hammarlund] AADE DFD1 for SP-600 question

[Al Parker]

Hi Folks,
    Andy, how'd you fair thru this hurricane?
    I have an SP-600 that I'm just finishing up, so put the scope on the 2
spots that Phil tried.
    On the plate tap, the one that's avaliable at the FCU switch, the 3
low bands, where it's single conversion, were rich in harmonics, and the
sig. varied from abt 2 to 4v p-p.  The 3rd band, 3.5-7.4 +-, had less
harmonic content, but like Andy says, the BC band's a mess.  I didn't ck
how much the freq. pulled.  The top band dropped way down in voltage at
the top half.  The 3 upper bands seemed pretty pure in content.
    Taking it at the grid, with a 10pf cap to the 10x scope probe, I see a
varying 8 to 11v p-p across all bands (exc. the top band which drops to
abt 5v at the hi end}, with it lowest at the high end of 7.4-14.8, and
varying unevenly, but not widely, across the 2 upper bands.  Freq. pulling
was severe.  There did not seem to be any harmonic content on any band
taken at this point.
    Hope I made that all fairly clear & it's of some interest.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info

----- Original Message ----- 
From: "James A. (Andy) Moorer" <jamminpower at earthlink.net>
To: "Philip Atchley" <beaconeer at sbcglobal.net>;
<hammarlund at mailman.qth.net>
Sent: Monday, August 29, 2005 2:37 PM
Subject: Re: [Hammarlund] AADE DFD1 for SP-600 question


> That is the correct place to tap the local oscillator - just on the wire
> that comes out of the RF deck and goes to the FCU.
>
> It WILL change the frequency of oscillation! Rather than using a
capacitor,
> I would just take an insulated wire from your preamplifier and twist it
> around the wire from the VFO. That makes a 1-2 pf joint. You will need
to
> touch up the calibration of the VFO after you do this.
>
> On the lower bands (500 kHz to maybe 8 MHz), the VFO output has all
kinds of
> harmonics. The VFO signal on the broadcast band is a mess. There is not
much
> you can do about it - no amount of changing the 6C4 oscillator will
help.
> The only thing that would help would be another tank circuit.
>
> That's all I know about it. I don't know what the AADE uses as its input
> stage. Best I can suggest is to put some high-frequency rolloff on the
> preamplifier and see if that helps.
>
> James A. (Andy) Moorer
> www.jamminpower.com
>
> ----- Original Message ----- 
> >
> > 1.  FIRST I tried tapping the plate circuit of the oscillator, first
at
> > the plate of the tube itself, and then at the wire that comes out to
the
> > VFO/Xtal oscillator switch.  Various capacitors from 1pF to 5pF were
> > tried. Tapping the signal at either of those points seemed to produce
the
> > same results.  A usable display up to about 43MC.  HOWEVER, the two
lowest
> > bands read accurately at the low end of the dial, but by about
midscale
> > (900KC on band 1) the readout suddenly jumped to a high reading and it
> > appeared that it was actually reading the 2nd harmonic of the LO!
> >
>