[GreenKeys] 28 loop supply transformer

[WA5CAB--- via GreenKeys]

Ken, et al,

I haven't designed a transformer in eons and have forgotten the actual 
numbers (and am not going to pull out Radiotron Designers Handbook to look them 
up).  But one of the important criteria in the design is the cross section 
of the core in the direction of the stack height.  Theoretically, if the 
design required 1 square inch of core area, you could make the center bar of the 
"E" 1/8" wide and the stack 8" high.  Of course, for several other practial 
reasons, you wouldn't want to do this.  The coils are (or used to be) wound 
on some sort of supported bobbin, and in a high speed winding machine, a 
square bobbin has some advantages (mainly wire tension and velocity 
fluctuations).  It probably isn't normal to start with footprint area in the design 
but it's my guess that that's what happened here.  The magnetic flux density 
in the core doesn't much care what the aspect ratio is.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 12/28/2014 07:55:05 AM Central Standard Time, 
ksweek at mindspring.com writes: 
> Something I have been wondering about for quite a while. The 
> transformer on the model 28 loop supply has a extremely high 
> lamination stack height verses footprint. Very unusual as I have not 
> seen this extreme in many decades of electronics work. I would have 
> thought there was some optimum lamination LxW size verses winding 
> cross sectional size but seems footprint size was the driving 
> consideration in this case. Do not know what the loop supply current 
> rating is but it must be rather high. What on a 28 would this supply 
> be powering other than the loop? Solenoids?
> 
> Just curious and am thinking someone on this list can fill in the blanks.
> 
> Ken S
> 
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