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

[Paul Staupe]

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