[ARC5] Using SCR-274N

[Dennis Monticelli]

I have fancied going the crystal filter route with the BC-453 (with
converter ahead for the ham bands).  Unfortunately, 85KHz resonators are
not only hard to find, then are very high in impedance. The hi-Z makes them
hard to graft into the IF chain without a lot of loss.  It can be done, but
it takes more work to do it in such a manner that it is easily reversible.
 A better route is probably using a fast op amp configured as an active
filter.  You can use a modern hi-speed op amp these days at 85KHz and still
get good Q.  It would be small and could run off a step-down from the DC
filament voltage.  I would experiment with this if I had the time.

Dennis AE6C


On Thu, Mar 28, 2013 at 5:19 PM, Bill Cromwell <wrcromwell at gmail.com> wrote:

> On Thu, 2013-03-28 at 17:35 -0400, Geoff wrote:
>
> >
> > A pair of surplus crystals and a few other small parts would help narrow
> the
> > bandpass on the wide open sets. It could all be done with a couple of
> tacked
> > in solder lug strips and easy to reverse. I havent looked at what is
> > actually available but it wouldnt hurt to look.
> >
> > Slight regeneration of an IF stage would also narrow it a bit without
> that
> > extreme hollow sound. No parts required maybe, just a gimmick feedback
> cap
> > grid to plate.
> >
> > A BC-454/455 that has already been bandspreaded could become a very nice
> CW
> > radio with minimal work. I believe Ken also mentioned that the 454 IF
> > transformers look possible to seperate the coils a bit.
> >
> > Carl
> >
>
> Hi Carl,
>
> I thought about that, too. I have built some xtal filters for receiver
> projects. The xtals that I used are higher in the HF range. If I find
> that xtals in the ranges of those IFs are not too hard to get I'll be
> going there.
>
> 73,
>
> Bill  KU8H
>
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