[HBR] Looking for some parts, leads welcome..

[Peter Bertini]

On Sun, Sep 21, 2008 at 3:45 PM, Walt Hutchens <waltah at earthlink.net> wrote:
>>
> Four 85 kcs IFTs from R-23/ARC-5 in two pairs (single 2nd IF stage) gives about the
> maximum selectivity that you can use for SSB with all the rods pulled
> up; it's a bit tight (but useable) for AM if you tune to one sideband
> or the other.  With rods pushed down it'll be fine for AM.  You
> cannot, however, move the rods up and down frequently -- the mechanism
> isn't designed for that.
>

> Walt
> KJ4KV
>

Walt

I would replace the fiber rods with brass welding rod and use a rack
and pinion mechanism
to move the coupling up and down. It isn't rocket science, and like I mentioned
Silvertone used link driven IF transformers for variable selectivity
settings in home
receivers back in the 1930s. Whether it is worth the effort, or
whether the idea is even
worth pursuing is probably open for discussion; not that it can or
can't be done in a
manner that works mechanically...

The only thing I'd question is how the selectivity curves on the
different IFTs would track
each other..  Esp. with cascaded IFs at the front of the strip and
single IFTs following
at the rear. The mechanical part would be easy, whether the results would be as
expected I am not so sure. It would be nice to have a good shape factor for AM
bandwidth, and a relative sharp peaked response for CW. Maybe I should
just settle
for the Q-Multiplier and leave it at that.

Matched crystals in the 1600 to 1700 kc range might allow for some
simple ladder filters
for CW and SSB reception, I'm aware of the limitations on lattice
crystal filters and there
are other options, such as the pair used in the HR-10 and other Heath
receivers. There must
be junkers out there.

 None of this is etched in stone, but I am mentally running
through all of the options. I'm almost tempted to build the RX in sub
assemblies, to permit
playing with different ideas for the IF (and sweeping them) to see the effects
before committing to chop up an expensive chassis.

Pete k1zjh