Jim,
I have the 208A CW Filter/Variable Notch Filter accessory for my Argonaut
515 but unfortunately, not the schematic.
For what it's worth, the IC's are RN4136N and used by both the cw filter
and the notch filter. Finding one (or an equivalent) over twenty years
after the fact might be quite a quest.
Instead of homebrewing a cw filter, you might consider adapting an old MFJ
CWF-2 active audio filter. Typically a $5.00 fleamarket item these days, it
uses two IC 747's to provide 180, 110 and 80 hz bandwidths. Nice skirts too!
I hardwired a CWF-2 into an Argonaut 505 and it did a super job with that
rig. It actually performed much better than the accessory 208 accessory
filter that went with the follow-up Argonaut 509.
In my experience, the CWF-2 and 208A are very close in performance though
the latter also includes the notch filter.
Good luck,
de Dave, NF0R nf0r@slacc.com
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