[ARC5] ARC-5/SCR-274-N IF Coil Mod

[Kenneth G. Gordon]

On 6 Mar 2014 at 16:35, D. Platt wrote:

> After a learning curve with the first coil, I found that the best way 
> (sic) was to remove the long screw that holds the coil group together.  
> Then, I carefully jigger the lower ceramic spacer out.  At this point, I 
> carefully heat and slide the wires from the _lower_ coil bobbin down a 
> bit to provide some slack.  I then move the lower bobbin downward about 
> 1/2".  I then replace the long screw up through the lower bobbin and 
> then up through the sleeved upper portion and replace the tiny nut.  To 
> hold everything in place, I used a drop of epoxy to the upper and lower 
> bobbins and the long screw.  Its solid enough and holds alignment.

OK. I did essentially the same thing until it came time to hold the bobbins in 
place: at that point, I went to both the local hardware store and to the local 
hobby shop and bought two different sizes of nylon washers and/or plastic 
"beads". I first used one of the plastic beads. I then used a piece of 4-40 
threaded rod to hold the entire assembly together. Sounds like my method is 
overkill. (Why am I not surprised?). I can more easily "adjust" the spacing 
with the nylon washers since they are thinner than the beads.

>  I 
> believe that once you do one of these, the others will be a lot easier.  
> I've been talking with Breck, K4CHE and his experience with this mod.  
> He got some very good selectivity curves on his.

I would really LOVE to see those!

>  Now, what I will do is 
> look up the audio mod in ER.

Now, what is that? I was not aware of that. Do you know which issue of ER that 
was in?

My audio mod is to replace R-20, the 2 megohm grid resistor at the 12A6 with a 
2 megohm audio taper pot, connecting the output side of C-29 to the wiper of 
the pot. This works very well to add an AF gain control to the receiver.

>  Also, I recall Norm (N3RZU) talking about 
> this method a number of years ago, back when we used to work 
> together.    Oh... before I forget. I mentioned this to Breck, but if I 
> reduce the B+ on this receiver to about 150v (down from 220v), the thing 
> seems to provide a lot more output?  I can't figure that, yet.

Gee...that IS weird!

>  This one 
> is also re-capped and, yes, I did all three coils.

OK. Kewel! Please do keep us informed of your results. And thanks a heap for 
doing this.

vy 73,

Ken W7EKB