Re: NC-190 Ferrite Filter questions


"Litzendraht" <k5cey@xxxxxxxx> wrote in message
news:1137033521.864750.275290@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> John,
> Your test equipment sure is classic. (Viva La BC-221). I use one
> myself. Are you reading the freq directly from the vernier dial on the
> 221? Of course if you have the book and trust your 221, that should be
> close enough. But a counter would be comforting.
> The BC-221 was a recent eBay purchase. They used them in school in
the early 60's and I thought it would be fun to have. The shafts
slipped on 2 variable cap trimmers inside allowing the plated to short.
Fixed 'em with super glue.
> I have an NC-270 and assuming that the filter circuitry is the same as
> your 190.
>
> Is your receiver working OK and you're just doing a fine alignment, or
> are there other issues?
> It was almost dead when I got it. wireing errors, wrong miswired
resistor in PS, bad 0B2, shorted coax under chassis. had to take a IF c
an apart and bust out a stuck slug, slipping dial. Now it's working but not
perfect. I've got the alignment better than it was. At first I just
peaked the IF's where they were and didn't touch the ferrite filters. Got it
to a point and let it sit for a few months. It seem like other
stations are trying to come in, other than what it's tuned to. I haven't
been able to tell if it's poor selectivity, images or overloading.
Writeing this and thinking about it is makeing me suspect those bypass caps.

> Where are you injecting the 230 kc signal?
At the middle sec of the main tuning cap, the input of the 1st
mixer.
>
> Are the two threaded rods in the filter backed all the way out and
> still won't hit 230 kc? I'm sure you're aligning the other 230 kc tuned
> circuits along with the filter.
> They peak before the end of travel but at 230kc as I reach the
peak it's not at the end yet, and keep turning it out to the end it don't go
down. Its like the peak is at the point where the slug is so far out it's
not makeing any more differance. 227 is as close as I can get to
230 and peak both coils.. I'm gonna clip in some extra bypass caps and see
what happens.

> If there has been a change in the ferrite characteristics as Chuck
> mentioned, possibly those two silver mica caps (3900 pf in the NC-270)
> could be replaced with a slightly lower value. But I don't think that
> type of change is likely here. An R-390 linear PTO would seem to be
> much more critical.
>
> John
>


.

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