[HBR] New member from Brazil

[Walt Hutchens]

Carlos said:
> Like I said, the biggest problem here is to find all the parts, mainly a
> adequate variable capacitor, trimmers and the dial.

A few things occur to me.

1. Vacuum tube auto radios were often built with 262 kcs IFs, thus
junker auto sets from the 1950's-60's might be a source.

2. Ham band only tuning (but not band imaging) is obtainable with the
main tuning cap from an FM receiver, in the U.S., 88-108 Mcs.  Again,
a junk set might provide what you need and (possibly) a dial mechanism
that could be adapted.

3. If you do 80-40M lband imaging with an IF of 5500 kcs (or so) -- this
requires a crystal filter of some sort, OR double conversion -- then
the 1st oscillator tunes 1500-2000 kcs. This is easily done with the
main tuning cap from a junk BC receiver. Don't knock this setup for
stability, either: The oscillator is very high-C and if well designed,
will drift something like 1 kcs before you do any sort of temperature
compensation and require no voltage regulation.

The front end -- which tunes ~3500-7300 kcs to select the band -- can
be tuned with a second BC cap.

I have a set with this design which uses a push-pull oscillator
driving a push pull mixer (both dual triodes) to give single-end IF
output.  The oscillator is so solid that I am using AGC on the mixer
as well as the two IF stages without pulling that's noticeable on SSB.
With three controlled stages, the AGC performance is excellent and
with no RF stage and a triode mixer, there's no problem with front
end overload.

This design does have a spurious response where the third harmonic of
the oscillator passes through the 5500 kcs IF.

You could use a 2nd IF of 262 kcs using three auto radio IFTs and get
tolerable performance -- perfectly adequate for AM, or (with audio
filter) CW.  This would require one IF stage at 5500 with fairly high Q
coils to control images.

Or using a half-lattice crystal filter (IF can be shifted slightly
according to what you can find) you can get excellent selectivity
without another conversion and extra stage. There are MANY kinds of
WW-II surplus crystals in that range.

I agree with Ian that the Super SimpleX and 2X4+1 designs are a useful
starting point.

Welcome aboard, Carlos!

Walt
KJ4KV