I am searching for part 1 of Linsley Hoods's 1986 3 articles for
Electronics & Wireless World.
I have paper copies of part 2 and 3, which contain basics if direct
conversion process, with block diagrams.
The "practical" block diagram shows 4 chips,
74H04, VCO,
74H74, Divide by two,
74H86, Wxclusive OR,
MC1496, Phase detector.
Linsley has RF input to 1:1 RFT, untuned, to 3N201 with AGC then
second RFT with 400pF tuning gang, then
to second 3N201 + AGC with third RFT taken to input of phase detector.
VFO 74HO4 has coil plus 390p across coil, plus 30pF trimmer, and all
with one end grounded. The varicap diode is a BB1058 in series with 1N
across coil and other C.
The whole BC band is thus tuned, and oscillator F adjusted by dc fed
to varicap diode via 220k, so a long time constant exists with 220k
&1N.
So it seems it IS POSSIBLE to tune the whole BC band between 550 and
1,700kHz.
Linsley says it would have been good to have a 3 gang tuning cap but
they are hard to find. I have plenty though.
There are numerous other ICs for the radio.
I also came across Mike Gruber's article at
http://www.olifantasia.com/projects/...9209qex009.pdf
Worth a read. But no tubes, and very complex, although some will say
its terribly simple.
Patrick Turner.