[R-390] Z 503... "non-A" vs. "A"

[ToddRoberts2001 at aol.com]

Hi Paul,
>From what I can tell, electrically  the Z-503 from both the R-390 and R-390A
are nearly identical so one from the  "A" model could be substituted  in 
the non-A version. Like you mentioned  one pulled from an "A" model should be 
much cheaper as they are a lot more  plentiful. 

I have also noticed that some versions of the Z-503 have an  adjustment 
hole in the top of the can and others have no hole for adjustment for  some 
reason. I have an early Collins R-390A that has no hole in the can but a  later 
version Motorola that does have a hole in the top of the can for slug  
adjustment. Someone could always drill a hole in the top of the can to allow for 
 adjustment of the slug if they have the version without the hole and 
wanted to  make sure the coil was peaked.  The slugs in both "A" versions are the 
same  - adjustable with a hex tool.

I think one could get a shielded inductor,  small value mica cap and a small
trimmer capacitor from Mouser and build a  "new" Z-503 for under $5 bucks.
Instead of using an adjustable inductor use a  small trimmer cap to "peak" 
the coil. Electrically the result should be the  same.

73 - Todd WD4NGG