[Hallicrafters] NC 270 product detector and VFO

[Glen Zook]

Maybe because the NC-270 really doesn't have much of a
product detector.  According to the manual (and this
is verified by looking at the schematic) the last i.f.
stage is "converted" into a product detector.  What is
done is that the BFO is activated and is applied to
the cathode of V5 the last i.f. stage.  The audio is
then taken off of the B+ side of the primary of the
last i.f. transformer.  For AM there is a tube diode
that comes off the secondary of the last i.f.
transformer.  The high side of the volume control is
switched between the "product detector" and the diode
detector.

The "S" meter adjust is off of the same V5 6BA6
cathode as where the BFO signal is applied.

The r.f. gain control goes to the cathodes of the r.f.
amplifier and the last 2 i.f. stages (including the
"product detector").  Frankly, in my opinion, pretty
much a Walt Disney production.  

I had an NC-270 for a short period of time.  It wasn't
a good performing receiver.

The oscillator operates 2215 KHz higher in frequency
on all bands but 6 meters.  It really doesn't have a
"VFO" like the more modern receivers.  Each band is
calibrated separately and the frequency of the
oscillator is going to range from about 5 MHz to about
32 MHz for the bands 80 meters through 10 meters.  I
believe that the 6 meter band is going to range
between 48 MHz and 52 MHz.

Glen, K9STH


--- Joseph Trombino Jr <w2kj at bellsouth.net> wrote:

I notice that when receiving strong SSB sigs the
receiver audio distorts and I have to turn down the RF
gain to make the signal readable.
 
I thought product detectors eliminated this phenomenom
(there's one in the NC 270).....is this the typical
behavior of the NC 270 or do I have a problem???
 
Also, does anyone know the range of the VFO in this
receiver???  The dial calibration is off so I would
want to align the VFO to the proper range.







Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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