[ARC5] Selectivity and the BC-455

[Kenneth G. Gordon]

On 24 Oct 2014 at 16:52, WA5CAB--- via ARC5 wrote:

> Here is, as saliors used to say, the "straight skinny".  I have and have 
> just gone through the manuals on all Type-K derived Command Sets.  All IFT's 
> in all models of all sets have two coils in all IFT's.  In all IFT's up 
> through 1415 KC, both the primary and the secondary coils are pie-wound and both 
> are tuned.
> 
> In all 4200 KC and all 2830 KC IFT's except those in R-27/ARC-5, the 
> primary coil is single layer close wound and is tuned.  The secondary is pie-wound 
> and untuned (or fix tuned).  In all IFT's in all R-27/ARC-5 (both before 
> and after 01 January 1945), the primary and secondary are both pie-wound and 
> both are tuned.

Yes. I just disassembled a 1st IF can from a badly hacked BC-455B I have 
here. The numbers on all the IF cans are 7277, 7278, and 7279.

The one I disassembeled DOES have two coils, a pi-wound and a single-
layer coil, but there is no way to separate them as Jeep has done with 
the 1415 Khz coils. Both coils are wound on a single form of what looks 
like phenolic and due to the length of the single-layer coil, there 
wouldn't be enough room to separate them, even if they were on separate 
forms.

My ancient memory either remembered this inability to move the coils as a 
single, "fat" pie-wound coil which looked tapped, or maybe I had some 
weirdo ham-hacked IF can which was built as I remember it.

What I CAN do is to take all the 2830 KHz IF cans I have, about 30 of 
them, open them all up and see if I can find the one I remembered as 
being a single, fat, piewound coil. There probably wasn't one.
 
> Probably someone with the necessary parts and the time should take a 
> BC-455, carefully alingn it, and measure the 6db and 60db bandwidths.  Then 
> substitute all three IFT's with a set from an R-27, re-align it and repeat the 
> bandwidth tests.

Yes. I think that would be extremely interesting.

Ken W7EKB