You will probably find that the Doug DeMaw approach will make the tuning
rather non-linear.
Years ago a slip of the soldering iron destroyed C4, 200 pf, which is in
parallel with the tuning capacitor (365 pf or so) in the VFO of my PM3A. I
replaced it with 220 pf in parallel with a further 470 pf. Just putting in
680 pf would have been good too, of course. Then I retuned the slug in the
inductor so that tuning got back to 7.00 Mhz on the bottom end. The tuning
rate was about 22kHz per turn on the bottom end of 40M with good linearity.
The dial covered about 175 kHz on 40M. You could also rip out a bunch of
plates from the tuning cap as an alternate approach for bandspreading - ah,
for the good old days!
Aside from breakthrough by the 40M SW stations, the real problem with the
standard PM3A is lack of RX offset or RIT. In my case I went all out and
added Dual RIT (to dodge the audio image QRM), changed all the slide
switches to toggle switches after they went intermittent, put in a new front
end, added a 4-pole audio filter, etc. As my buddy, VE2AYL, said at the
time, "It sure looks modified." On the other hand, it worked FB and I did
work about 175 stations on FD one year running 1B Battery / 1op with my PM3A
and a 40/20 multiwire dipole.
Ten Tecs were made to modify!
Tom Hamblin, VA3TH, VE3HIE, sine HN
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