[ARC5] Selectivity and the BC-455

[Ian Wilson]

Update on my measurements: I went through my ARC-5 spares box and
discovered three 7277 (1st) IFTs. On closer inspection, two of these have
been modified. The third unit had unbroken red paint over the screws so
I think it's safe to assume this one is kosher.

The pi winding in the intact 7277 measures about 2mH. This is drastically
different from the other two: 60uH and 180uH. My guess is that someone
was trying to turn the second winding into a tuned one.

So, I no longer think that the pie-wound winding was meant to resonate
approximately with the input capacitance of the second stage.

73, ian K3IMW


On Fri, Oct 24, 2014 at 5:55 PM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 24 Oct 2014 at 18:39, Joel R Roberts wrote:
>
> > Hello Ken and Brian, On page 171, figure 42 shows the graphic of the
> > BC-455-A IF cans as only having one coil in all three cans. These are
> > the diagrams for the 2830kc IF cans 7277, 7278 and 7279 on the part
> > numbers.
>
> Actually, Joel, if you look more carefully at those drawings, you will see
> a
> representation of that single-layer coil, labled L-6, L-8, and L-10 . So,
> Bob is
> correct: there ARE two coils in there. Just not two pi-wound jobs.
>
> > Also in looking at the tables in Gordon White's article
> > "Command Set Receivers for All Frequencies- The Easy Way" it shows the
> > ARC-5 models have 2 coils while the 274-N 6-9.1, 9-13.5, 13.5- 20 and
> > the 20-27 all have only one coil in the IF cans.
>
> Ah! I had forgotten about that! Yes. You're correct as to what it says.
> However, those may have been an early model IFT.
>
> > Lower Frequency IF cans
> > have 2 coils, some fixed and some adjustable.
>
> Hmmm....gotta go re-read Gordon's article.
>
> Ken
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