[Amps] Winding plate inductors - No sweat

[RFlabnotes at aol.com]

The venerable formula for a solenoidal inductor has been with us for over 60 
years, and is really all you need. I have wound hundreds of coils based on 
this formula and whenever I have taken the time to verify the result, it was 
always within about 10%. You couldn't ask for much more. 

The most convenient form of this formula is as follows. Make a copy of it and 
hang it up in your shop. All units are in inches.

L(uh)=d * N(squared)/[18+40l/d]     d=diameter  l=length  N=#turns

The formula starts to lose accuracy when the coil becomes too fat or too 
skinny, but is fine for average coils with l/d ratios of 2-10. It is relatively 
independent of wire size because within the range of wires typically used, the 
internal inductance of the wire is such a small fraction of the total 
inductance that its variation with diameter doesn't mean much/

In the last amplifier I built, I used this for winding the coils for both 
plate and input circuits, using inductance values based upon standard 
calculations for Pi-L  and LC networks. When I fired the amp up, everything tuned up 
perfectly the first time. 

73 
Eric von Valtier K8LV