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

[rbethman]

Paul,

Todd's solution is only good for the R-390A/URR.  This is one of the 
Cost Reduction Changes that grew into the production of the R-390A/URR.

The fact of the matter is, the R-390A/URR IF transformers are ALL 
identical with a higher Q than what they first went to the Signal Corps 
with.

I'm interested in Todd's solution.  If he can build it as a repeatable 
item, and it can work in ALL IF transformer positions, there will be a 
BIG sigh of relief!

Bob - N0DGN

On 4/3/2011 4:50 PM, Paul Staupe wrote:
> Hi Todd,
>
> Thanks for doing the measurements of your Z-503 and sharing the results.  It
> looks as though a much cheaper alternative might be built with modern
> components.  After a lot of dead ends, I was lucky enough to find a non-A
> version from Fair Radio, however as you would expect, the price was high.
> ($45.00)
>
> I'm the guy who originally asked the question about Z-503 a few weeks ago.
> There seems to be some confusion about the "A" version and the non-A
> version, since Z-503 does the same thing (AGC) in both designs.
>
> I noticed in the non-A schematic that there's no L or C designation as in
> the "A" model (L 514 and C 563).  However, there is "82" next to the cap in
> the non-A schematic which I would expect means 82 pF.   Since you measured
> 84 pF on your Z-503, I'm wondering if they could be substituted for each
> other?
>
> I've got an Imperial from the '63 "A" contract, and the cans are close to
> the same size. I haven't taken the Z-503 apart from the Imperial, but from
> what others are saying, it's potted just like the non-A version, and also
> has a shield.  There is a slight difference in that the ferrite adjustment
> in the "non-A" is done with a screwdriver, and with an insulated hex tool in
> the "A" version.
>
> If the "A" version could be substituted for the non-A, that might be a
> solution for the unobtanium non-A version, since there are so many more
> junker "A" IF decks out there.  Just a thought....
>
> Best regards,
>
> Paul W0AD